配合另一篇文章食用~ # 一文了解promise generator async的原理
/**
* Copyright (c) 2014-present, Facebook, Inc.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/
var runtime = (function (exports) {
"use strict";
var Op = Object.prototype;
var hasOwn = Op.hasOwnProperty;
var undefined; // More compressible than void 0.
var $Symbol = typeof Symbol === "function" ? Symbol : {};
var iteratorSymbol = $Symbol.iterator || "@@iterator";
var asyncIteratorSymbol = $Symbol.asyncIterator || "@@asyncIterator";
var toStringTagSymbol = $Symbol.toStringTag || "@@toStringTag";
function define(obj, key, value) {
Object.defineProperty(obj, key, {
value: value,
enumerable: true,
configurable: true,
writable: true
});
return obj[key];
}
try {
// IE 8 has a broken Object.defineProperty that only works on DOM objects.
define({}, "");
} catch (err) {
define = function(obj, key, value) {
return obj[key] = value;
};
}
function wrap(innerFn, outerFn, self, tryLocsList) {
// If outerFn provided and outerFn.prototype is a Generator, then outerFn.prototype instanceof Generator.
var protoGenerator = outerFn && outerFn.prototype instanceof Generator ? outerFn : Generator;
var generator = Object.create(protoGenerator.prototype);
var context = new Context(tryLocsList || []);
// The ._invoke method unifies the implementations of the .next,
// .throw, and .return methods.
generator._invoke = makeInvokeMethod(innerFn, self, context);
return generator;
}
exports.wrap = wrap;
// Try/catch helper to minimize deoptimizations. Returns a completion
// record like context.tryEntries[i].completion. This interface could
// have been (and was previously) designed to take a closure to be
// invoked without arguments, but in all the cases we care about we
// already have an existing method we want to call, so there's no need
// to create a new function object. We can even get away with assuming
// the method takes exactly one argument, since that happens to be true
// in every case, so we don't have to touch the arguments object. The
// only additional allocation required is the completion record, which
// has a stable shape and so hopefully should be cheap to allocate.
function tryCatch(fn, obj, arg) {
try {
return { type: "normal", arg: fn.call(obj, arg) };
} catch (err) {
return { type: "throw", arg: err };
}
}
var GenStateSuspendedStart = "suspendedStart";
var GenStateSuspendedYield = "suspendedYield";
var GenStateExecuting = "executing";
var GenStateCompleted = "completed";
// Returning this object from the innerFn has the same effect as
// breaking out of the dispatch switch statement.
var ContinueSentinel = {};
// Dummy constructor functions that we use as the .constructor and
// .constructor.prototype properties for functions that return Generator
// objects. For full spec compliance, you may wish to configure your
// minifier not to mangle the names of these two functions.
function Generator() {}
function GeneratorFunction() {}
function GeneratorFunctionPrototype() {}
// This is a polyfill for %IteratorPrototype% for environments that
// don't natively support it.
var IteratorPrototype = {};
define(IteratorPrototype, iteratorSymbol, function () {
return this;
});
var getProto = Object.getPrototypeOf;
var NativeIteratorPrototype = getProto && getProto(getProto(values([])));
if (NativeIteratorPrototype &&
NativeIteratorPrototype !== Op &&
hasOwn.call(NativeIteratorPrototype, iteratorSymbol)) {
// This environment has a native %IteratorPrototype%; use it instead
// of the polyfill.
IteratorPrototype = NativeIteratorPrototype;
}
var Gp = GeneratorFunctionPrototype.prototype =
Generator.prototype = Object.create(IteratorPrototype);
GeneratorFunction.prototype = GeneratorFunctionPrototype;
define(Gp, "constructor", GeneratorFunctionPrototype);
define(GeneratorFunctionPrototype, "constructor", GeneratorFunction);
GeneratorFunction.displayName = define(
GeneratorFunctionPrototype,
toStringTagSymbol,
"GeneratorFunction"
);
// Helper for defining the .next, .throw, and .return methods of the
// Iterator interface in terms of a single ._invoke method.
function defineIteratorMethods(prototype) {
["next", "throw", "return"].forEach(function(method) {
define(prototype, method, function(arg) {
return this._invoke(method, arg);
});
});
}
exports.isGeneratorFunction = function(genFun) {
var ctor = typeof genFun === "function" && genFun.constructor;
return ctor
? ctor === GeneratorFunction ||
// For the native GeneratorFunction constructor, the best we can
// do is to check its .name property.
(ctor.displayName || ctor.name) === "GeneratorFunction"
: false;
};
exports.mark = function(genFun) {
if (Object.setPrototypeOf) {
Object.setPrototypeOf(genFun, GeneratorFunctionPrototype);
} else {
genFun.__proto__ = GeneratorFunctionPrototype;
define(genFun, toStringTagSymbol, "GeneratorFunction");
}
genFun.prototype = Object.create(Gp);
return genFun;
};
// Within the body of any async function, `await x` is transformed to
// `yield regeneratorRuntime.awrap(x)`, so that the runtime can test
// `hasOwn.call(value, "__await")` to determine if the yielded value is
// meant to be awaited.
exports.awrap = function(arg) {
return { __await: arg };
};
function AsyncIterator(generator, PromiseImpl) {
function invoke(method, arg, resolve, reject) {
var record = tryCatch(generator[method], generator, arg);
if (record.type === "throw") {
reject(record.arg);
} else {
var result = record.arg;
var value = result.value;
if (value &&
typeof value === "object" &&
hasOwn.call(value, "__await")) {
return PromiseImpl.resolve(value.__await).then(function(value) {
invoke("next", value, resolve, reject);
}, function(err) {
invoke("throw", err, resolve, reject);
});
}
return PromiseImpl.resolve(value).then(function(unwrapped) {
// When a yielded Promise is resolved, its final value becomes
// the .value of the Promise<{value,done}> result for the
// current iteration.
result.value = unwrapped;
resolve(result);
}, function(error) {
// If a rejected Promise was yielded, throw the rejection back
// into the async generator function so it can be handled there.
return invoke("throw", error, resolve, reject);
});
}
}
var previousPromise;
function enqueue(method, arg) {
function callInvokeWithMethodAndArg() {
return new PromiseImpl(function(resolve, reject) {
invoke(method, arg, resolve, reject);
});
}
return previousPromise =
// If enqueue has been called before, then we want to wait until
// all previous Promises have been resolved before calling invoke,
// so that results are always delivered in the correct order. If
// enqueue has not been called before, then it is important to
// call invoke immediately, without waiting on a callback to fire,
// so that the async generator function has the opportunity to do
// any necessary setup in a predictable way. This predictability
// is why the Promise constructor synchronously invokes its
// executor callback, and why async functions synchronously
// execute code before the first await. Since we implement simple
// async functions in terms of async generators, it is especially
// important to get this right, even though it requires care.
previousPromise ? previousPromise.then(
callInvokeWithMethodAndArg,
// Avoid propagating failures to Promises returned by later
// invocations of the iterator.
callInvokeWithMethodAndArg
) : callInvokeWithMethodAndArg();
}
// Define the unified helper method that is used to implement .next,
// .throw, and .return (see defineIteratorMethods).
this._invoke = enqueue;
}
defineIteratorMethods(AsyncIterator.prototype);
define(AsyncIterator.prototype, asyncIteratorSymbol, function () {
return this;
});
exports.AsyncIterator = AsyncIterator;
// Note that simple async functions are implemented on top of
// AsyncIterator objects; they just return a Promise for the value of
// the final result produced by the iterator.
exports.async = function(innerFn, outerFn, self, tryLocsList, PromiseImpl) {
if (PromiseImpl === void 0) PromiseImpl = Promise;
var iter = new AsyncIterator(
wrap(innerFn, outerFn, self, tryLocsList),
PromiseImpl
);
return exports.isGeneratorFunction(outerFn)
? iter // If outerFn is a generator, return the full iterator.
: iter.next().then(function(result) {
return result.done ? result.value : iter.next();
});
};
function makeInvokeMethod(innerFn, self, context) {
var state = GenStateSuspendedStart;
return function invoke(method, arg) {
if (state === GenStateExecuting) {
throw new Error("Generator is already running");
}
if (state === GenStateCompleted) {
if (method === "throw") {
throw arg;
}
// Be forgiving, per 25.3.3.3.3 of the spec:
// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-generatorresume
return doneResult();
}
context.method = method;
context.arg = arg;
while (true) {
var delegate = context.delegate;
if (delegate) {
var delegateResult = maybeInvokeDelegate(delegate, context);
if (delegateResult) {
if (delegateResult === ContinueSentinel) continue;
return delegateResult;
}
}
if (context.method === "next") {
// Setting context._sent for legacy support of Babel's
// function.sent implementation.
context.sent = context._sent = context.arg;
} else if (context.method === "throw") {
if (state === GenStateSuspendedStart) {
state = GenStateCompleted;
throw context.arg;
}
context.dispatchException(context.arg);
} else if (context.method === "return") {
context.abrupt("return", context.arg);
}
state = GenStateExecuting;
var record = tryCatch(innerFn, self, context);
if (record.type === "normal") {
// If an exception is thrown from innerFn, we leave state ===
// GenStateExecuting and loop back for another invocation.
state = context.done
? GenStateCompleted
: GenStateSuspendedYield;
if (record.arg === ContinueSentinel) {
continue;
}
return {
value: record.arg,
done: context.done
};
} else if (record.type === "throw") {
state = GenStateCompleted;
// Dispatch the exception by looping back around to the
// context.dispatchException(context.arg) call above.
context.method = "throw";
context.arg = record.arg;
}
}
};
}
// Call delegate.iterator[context.method](context.arg) and handle the
// result, either by returning a { value, done } result from the
// delegate iterator, or by modifying context.method and context.arg,
// setting context.delegate to null, and returning the ContinueSentinel.
function maybeInvokeDelegate(delegate, context) {
var method = delegate.iterator[context.method];
if (method === undefined) {
// A .throw or .return when the delegate iterator has no .throw
// method always terminates the yield* loop.
context.delegate = null;
if (context.method === "throw") {
// Note: ["return"] must be used for ES3 parsing compatibility.
if (delegate.iterator["return"]) {
// If the delegate iterator has a return method, give it a
// chance to clean up.
context.method = "return";
context.arg = undefined;
maybeInvokeDelegate(delegate, context);
if (context.method === "throw") {
// If maybeInvokeDelegate(context) changed context.method from
// "return" to "throw", let that override the TypeError below.
return ContinueSentinel;
}
}
context.method = "throw";
context.arg = new TypeError(
"The iterator does not provide a 'throw' method");
}
return ContinueSentinel;
}
var record = tryCatch(method, delegate.iterator, context.arg);
if (record.type === "throw") {
context.method = "throw";
context.arg = record.arg;
context.delegate = null;
return ContinueSentinel;
}
var info = record.arg;
if (! info) {
context.method = "throw";
context.arg = new TypeError("iterator result is not an object");
context.delegate = null;
return ContinueSentinel;
}
if (info.done) {
// Assign the result of the finished delegate to the temporary
// variable specified by delegate.resultName (see delegateYield).
context[delegate.resultName] = info.value;
// Resume execution at the desired location (see delegateYield).
context.next = delegate.nextLoc;
// If context.method was "throw" but the delegate handled the
// exception, let the outer generator proceed normally. If
// context.method was "next", forget context.arg since it has been
// "consumed" by the delegate iterator. If context.method was
// "return", allow the original .return call to continue in the
// outer generator.
if (context.method !== "return") {
context.method = "next";
context.arg = undefined;
}
} else {
// Re-yield the result returned by the delegate method.
return info;
}
// The delegate iterator is finished, so forget it and continue with
// the outer generator.
context.delegate = null;
return ContinueSentinel;
}
// Define Generator.prototype.{next,throw,return} in terms of the
// unified ._invoke helper method.
defineIteratorMethods(Gp);
define(Gp, toStringTagSymbol, "Generator");
// A Generator should always return itself as the iterator object when the
// @@iterator function is called on it. Some browsers' implementations of the
// iterator prototype chain incorrectly implement this, causing the Generator
// object to not be returned from this call. This ensures that doesn't happen.
// See https://github.com/facebook/regenerator/issues/274 for more details.
define(Gp, iteratorSymbol, function() {
return this;
});
define(Gp, "toString", function() {
return "[object Generator]";
});
function pushTryEntry(locs) {
var entry = { tryLoc: locs[0] };
if (1 in locs) {
entry.catchLoc = locs[1];
}
if (2 in locs) {
entry.finallyLoc = locs[2];
entry.afterLoc = locs[3];
}
this.tryEntries.push(entry);
}
function resetTryEntry(entry) {
var record = entry.completion || {};
record.type = "normal";
delete record.arg;
entry.completion = record;
}
function Context(tryLocsList) {
// The root entry object (effectively a try statement without a catch
// or a finally block) gives us a place to store values thrown from
// locations where there is no enclosing try statement.
this.tryEntries = [{ tryLoc: "root" }];
tryLocsList.forEach(pushTryEntry, this);
this.reset(true);
}
exports.keys = function(object) {
var keys = [];
for (var key in object) {
keys.push(key);
}
keys.reverse();
// Rather than returning an object with a next method, we keep
// things simple and return the next function itself.
return function next() {
while (keys.length) {
var key = keys.pop();
if (key in object) {
next.value = key;
next.done = false;
return next;
}
}
// To avoid creating an additional object, we just hang the .value
// and .done properties off the next function object itself. This
// also ensures that the minifier will not anonymize the function.
next.done = true;
return next;
};
};
function values(iterable) {
if (iterable) {
var iteratorMethod = iterable[iteratorSymbol];
if (iteratorMethod) {
return iteratorMethod.call(iterable);
}
if (typeof iterable.next === "function") {
return iterable;
}
if (!isNaN(iterable.length)) {
var i = -1, next = function next() {
while (++i < iterable.length) {
if (hasOwn.call(iterable, i)) {
next.value = iterable[i];
next.done = false;
return next;
}
}
next.value = undefined;
next.done = true;
return next;
};
return next.next = next;
}
}
// Return an iterator with no values.
return { next: doneResult };
}
exports.values = values;
function doneResult() {
return { value: undefined, done: true };
}
Context.prototype = {
constructor: Context,
reset: function(skipTempReset) {
this.prev = 0;
this.next = 0;
// Resetting context._sent for legacy support of Babel's
// function.sent implementation.
this.sent = this._sent = undefined;
this.done = false;
this.delegate = null;
this.method = "next";
this.arg = undefined;
this.tryEntries.forEach(resetTryEntry);
if (!skipTempReset) {
for (var name in this) {
// Not sure about the optimal order of these conditions:
if (name.charAt(0) === "t" &&
hasOwn.call(this, name) &&
!isNaN(+name.slice(1))) {
this[name] = undefined;
}
}
}
},
stop: function() {
this.done = true;
var rootEntry = this.tryEntries[0];
var rootRecord = rootEntry.completion;
if (rootRecord.type === "throw") {
throw rootRecord.arg;
}
return this.rval;
},
dispatchException: function(exception) {
if (this.done) {
throw exception;
}
var context = this;
function handle(loc, caught) {
record.type = "throw";
record.arg = exception;
context.next = loc;
if (caught) {
// If the dispatched exception was caught by a catch block,
// then let that catch block handle the exception normally.
context.method = "next";
context.arg = undefined;
}
return !! caught;
}
for (var i = this.tryEntries.length - 1; i >= 0; --i) {
var entry = this.tryEntries[i];
var record = entry.completion;
if (entry.tryLoc === "root") {
// Exception thrown outside of any try block that could handle
// it, so set the completion value of the entire function to
// throw the exception.
return handle("end");
}
if (entry.tryLoc <= this.prev) {
var hasCatch = hasOwn.call(entry, "catchLoc");
var hasFinally = hasOwn.call(entry, "finallyLoc");
if (hasCatch && hasFinally) {
if (this.prev < entry.catchLoc) {
return handle(entry.catchLoc, true);
} else if (this.prev < entry.finallyLoc) {
return handle(entry.finallyLoc);
}
} else if (hasCatch) {
if (this.prev < entry.catchLoc) {
return handle(entry.catchLoc, true);
}
} else if (hasFinally) {
if (this.prev < entry.finallyLoc) {
return handle(entry.finallyLoc);
}
} else {
throw new Error("try statement without catch or finally");
}
}
}
},
abrupt: function(type, arg) {
for (var i = this.tryEntries.length - 1; i >= 0; --i) {
var entry = this.tryEntries[i];
if (entry.tryLoc <= this.prev &&
hasOwn.call(entry, "finallyLoc") &&
this.prev < entry.finallyLoc) {
var finallyEntry = entry;
break;
}
}
if (finallyEntry &&
(type === "break" ||
type === "continue") &&
finallyEntry.tryLoc <= arg &&
arg <= finallyEntry.finallyLoc) {
// Ignore the finally entry if control is not jumping to a
// location outside the try/catch block.
finallyEntry = null;
}
var record = finallyEntry ? finallyEntry.completion : {};
record.type = type;
record.arg = arg;
if (finallyEntry) {
this.method = "next";
this.next = finallyEntry.finallyLoc;
return ContinueSentinel;
}
return this.complete(record);
},
complete: function(record, afterLoc) {
if (record.type === "throw") {
throw record.arg;
}
if (record.type === "break" ||
record.type === "continue") {
this.next = record.arg;
} else if (record.type === "return") {
this.rval = this.arg = record.arg;
this.method = "return";
this.next = "end";
} else if (record.type === "normal" && afterLoc) {
this.next = afterLoc;
}
return ContinueSentinel;
},
finish: function(finallyLoc) {
for (var i = this.tryEntries.length - 1; i >= 0; --i) {
var entry = this.tryEntries[i];
if (entry.finallyLoc === finallyLoc) {
this.complete(entry.completion, entry.afterLoc);
resetTryEntry(entry);
return ContinueSentinel;
}
}
},
"catch": function(tryLoc) {
for (var i = this.tryEntries.length - 1; i >= 0; --i) {
var entry = this.tryEntries[i];
if (entry.tryLoc === tryLoc) {
var record = entry.completion;
if (record.type === "throw") {
var thrown = record.arg;
resetTryEntry(entry);
}
return thrown;
}
}
// The context.catch method must only be called with a location
// argument that corresponds to a known catch block.
throw new Error("illegal catch attempt");
},
delegateYield: function(iterable, resultName, nextLoc) {
this.delegate = {
iterator: values(iterable),
resultName: resultName,
nextLoc: nextLoc
};
if (this.method === "next") {
// Deliberately forget the last sent value so that we don't
// accidentally pass it on to the delegate.
this.arg = undefined;
}
return ContinueSentinel;
}
};
// Regardless of whether this script is executing as a CommonJS module
// or not, return the runtime object so that we can declare the variable
// regeneratorRuntime in the outer scope, which allows this module to be
// injected easily by `bin/regenerator --include-runtime script.js`.
return exports;
}(
// If this script is executing as a CommonJS module, use module.exports
// as the regeneratorRuntime namespace. Otherwise create a new empty
// object. Either way, the resulting object will be used to initialize
// the regeneratorRuntime variable at the top of this file.
typeof module === "object" ? module.exports : {}
));
try {
regeneratorRuntime = runtime;
} catch (accidentalStrictMode) {
// This module should not be running in strict mode, so the above
// assignment should always work unless something is misconfigured. Just
// in case runtime.js accidentally runs in strict mode, in modern engines
// we can explicitly access globalThis. In older engines we can escape
// strict mode using a global Function call. This could conceivably fail
// if a Content Security Policy forbids using Function, but in that case
// the proper solution is to fix the accidental strict mode problem. If
// you've misconfigured your bundler to force strict mode and applied a
// CSP to forbid Function, and you're not willing to fix either of those
// problems, please detail your unique predicament in a GitHub issue.
if (typeof globalThis === "object") {
globalThis.regeneratorRuntime = runtime;
} else {
Function("r", "regeneratorRuntime = r")(runtime);
}
}
大致介绍下
function* foo() {
yield "result1";
let res2 = yield "result2";
try {
yield "result3";
} catch (e) {
console.log("e", e);
}
return "result5";
}
const gen = foo();
gen.next();
gen.next();
gen.next();
gen.throw();
gen.next();
// 上面代码会被编译成下面的代码
var _marked = /*#__PURE__*/regeneratorRuntime.mark(foo);
function foo() {
var res2;
return regeneratorRuntime.wrap(function foo$(_context) {
while (1) {
switch (_context.prev = _context.next) {
case 0:
_context.next = 2;
return "result1";
case 2:
_context.next = 4;
return "result2";
case 4:
res2 = _context.sent;
_context.prev = 5;
_context.next = 8;
return "result3";
case 8:
_context.next = 13;
break;
case 10:
_context.prev = 10;
_context.t0 = _context["catch"](5);
console.log("e", _context.t0);
case 13:
return _context.abrupt("return", "result5");
case 14:
case "end":
return _context.stop();
}
}
}, _marked, null, [[5, 10]]);
}
var gen = foo();
gen.next();
gen.next();
gen.next();
gen["throw"]();
gen.next();
1. 初始化(只说涉及的一部分)
1.1 初始化 Gp(generator prototype) 是一个对象,有next,throw,return等方法,作为新生成generator 迭代器对象的原型
// invoke 就是next,throw,return方法, 内部会做判断
function defineIteratorMethods(prototype) {
["next", "throw", "return"].forEach(function(method) {
// 下面就相当于 prototype.next = function (arg) { this._invoke('next',arg) }
define(prototype, method, function(arg) {
return this._invoke(method, arg);
});
});
}
// 挂在在 Gp 原型上, 所以 Gp 上就有了3方法
defineIteratorMethods(Gp);
2. 给方法挂在原型
var _marked = /*#__PURE__*/regeneratorRuntime.mark(foo);
// 就是给传入的方法挂在一系列的原型 返回方法本身
exports.mark = function(genFun) {
if (Object.setPrototypeOf) {
Object.setPrototypeOf(genFun, GeneratorFunctionPrototype);
} else {
genFun.__proto__ = GeneratorFunctionPrototype;
define(genFun, toStringTagSymbol, "GeneratorFunction");
}
// !! 重点记一下 给传入方法的原型变更为 继承Gp的对象
genFun.prototype = Object.create(Gp);
return genFun;
};
3. regeneratorRuntime.wrap 介绍
// 第一个参数是 里层的foo$(主要执行的方法) 第二个参数是外层 foo
// self: 是 innerFn 的this指向
// tryLocsList [[5, 10]] 是个二维数组,因为可能有多个trycatch 每组都要记录try和catch所在代码的 case
function wrap(innerFn, outerFn, self, tryLocsList) {
// outerFn 就是上面mark改变原型过后的foo方法就是判断下原型挂上去没有
var protoGenerator = outerFn && outerFn.prototype instanceof Generator ? outerFn : Generator;
// 如果挂上去了 就把继承 Gp的对象 再继承一遍 简单说就是继承了 Gp 有了next等方法
// generator__proto__ -> {}.__proto__ -> Gp
var generator = Object.create(protoGenerator.prototype);
// 每个generator执行 内部都会维护一套状态(用来判断 执行到哪一步prev 下一步哪一步next 上一步的next传入值 sent 等等
var context = new Context(tryLocsList || []);
// The ._invoke method unifies the implementations of the .next,
// .throw, and .return methods.
// 最后挂载一个_invoke 就是上面第二步说的 next,throw实际调用的方法
// makeInvokeMethod创建一个invoke方法
generator._invoke = makeInvokeMethod(innerFn, self, context);
return generator;
}
4. makeInvokeMethod 生成next,throw,return方法
这个方法就比较大 去掉相对不重要的部分说明
// 作用就是返回一个 invoke 就是实际执行的next throw return
function makeInvokeMethod(innerFn, self, context) {
// 内部维护一个状态 state
// 类型是 string
// 枚举有 suspendedStart开始 suspendedYield(未执行到最后中间步) executing执行中 completed完成
var state = GenStateSuspendedStart;
return function invoke(method, arg) {
// 如果是完成状态 就直接返回 { value: undefined, done: true }
if (state === GenStateCompleted) {
if (method === "throw") {
throw arg;
}
return doneResult(); // { value: undefined, done: true }
}
// 每次执行都改变context的 method 和 arg, 把当前执行方法和参数覆盖上去
context.method = method;
context.arg = arg;
// 循环执行 执行到throw return等需要执行下一步的next或最后的case end 所以直接用循环
while (true) {
// 当执行的方法是 next 是 记录传入的值 赋值给 context的sent属性
// sent (next传入值) 下一次next switch case中可以通过context.sent获取
if (context.method === "next") {
context.sent = context._sent = context.arg;
} else if (context.method === "throw") {
// 当执行的方法是 throw时
if (state === GenStateSuspendedStart) {
// 如果是一开始就调用 throw方法 就会直接改变state为完成 抛出错误
// 所以generator第一次不执行next 直接执行throw 内部是无法捕获错误的
state = GenStateCompleted;
throw context.arg;
}
// 当throw 不是一开始就执行时这里简单说 详细看第五节
// 改变context.next到catch语句所在的地方 上面的案例就是next=10,[[3,10]] 下一次就直接执行 case10
// throw执行的 case10 后面没有中止语句return或者break所以会直接执行下一个 case 语句,相当于一次next (所以context.method改为next arg改为undefined)
context.dispatchException(context.arg);
} else if (context.method === "return") {
// 当执行的是return 就执行context的abupt方法
// 找到匹配位置的try catch对应的context.tryEntries并把错误信息存进去(存储每个trycatch位置和内容)
// abrupt 方法 会调用 context.complete方法
// complete 主要是改变context methe:return next:end(end就是最后一个case) 返回值赋值给context.rval 方法返回值 ContinueSentinel用来再次执行next的判断(下面)
// case end中执行的context.end方法 作用就是 改变done状态返回rval(return的返回值)
context.abrupt("return", context.arg);
}
// 改变状态为 执行中
state = GenStateExecuting;
// 这一步就是实际执行 innerFn的方法就是执行外面那个swich case的方法
// tryCatch 会捕获执行case的错误
// 正确返回{type:'normal;,arg:innerFn.call(self,context)}
// 错误返回{type:'throw;,arg:捕获到的错误}
var record = tryCatch(innerFn, self, context);
// 执行没出错时
if (record.type === "normal") {
//判断是否执行到最后一步 来赋值不同的state
state = context.done
? GenStateCompleted // 完成
: GenStateSuspendedYield; // 未完成
// 上面return执行的语句里有执行到一个context.complete方法 返回就是ContinueSentinel 当执行完return方法 赋值了错误值之后 重新启用循环执行最后的 case end 输入返回值 改变done状态为true 这时候在返回
if (record.arg === ContinueSentinel) {
continue;
}
// 正常next就直接返回执行的值
return {
value: record.arg,
done: context.done
};
} else if (record.type === "throw") {
// 如果执行innerFn的某个case语句直接报错了,会走到这里
// 改变状态为完成 改变方法为throw 改变参数为报错参数再走一遍循环
// 重新走throw方法 会改变 next为 end 因为没有被trycatch捕获(后面dispatchException中细说什么时候捕获)
// next 改为end 上面走innerFn 最后的end方法 执行context.stop方法 这里会判断会不会被捕获到 没有捕获到就直接抛出异常 运行结束
state = GenStateCompleted;
context.method = "throw";
context.arg = record.arg;
}
}
};
}
5. dispatchException throw的时候调用的处理异常
秃了秃了... 看删减版
// Context 原型上的方法
dispatchException: function(exception) {
// 如果generator已经结束了done为true 再执行throw方法会直接抛出错误
if (this.done) {
throw exception;
}
var context = this;
// 综合处理错误情况
function handle(loc, caught) {
// 改变错误值和type
record.type = "throw";
record.arg = exception;
// 改变next为catch所在case位置
context.next = loc;
// 当错误被捕获 就走里面代码 改变method为next
if (caught) {
context.method = "next";
context.arg = undefined;
}
return !! caught;
}
// context 初始化的时候会初始化一个记录错误的数组 tryEntries = [{tryLoc:'root',complettion:{type:'normal',arg:undefined}}]
// 上面的案例传入[[3,10]]会遍历这个数据把值复制到 tryEntries中
// 所以上面最后初始化后tryEntries=[{ tryLoc: "root",completion:{type:'normal'} },{tryLoc:3,catchLoc:10,completion:{type:'normal'}}]
// tryLoc 是try所在的case catchLoc是catch所在代码的case
for (var i = this.tryEntries.length - 1; i >= 0; --i) {
// 从后往前遍历
var entry = this.tryEntries[i]; //{tryLoc:3,catchLoc:10,completion:{type:'normal'}}
var record = entry.completion; // type 和 arg:就是错误值
// root是初始化第一个默认值 从后往前匹配的 如果没有匹配到 就说明错误没有被捕获
if (entry.tryLoc === "root") {
return handle("end");
}
// 当执行到某个case 改变会改变prev和next prev就是当前的执行case位置
// tryloc就是try里面代码所在的case位置
// try 小于等于当前执行的代码 说明代码在try里或后面
if (entry.tryLoc <= this.prev) {
var hasCatch = hasOwn.call(entry, "catchLoc");
var hasFinally = hasOwn.call(entry, "finallyLoc");
if (hasCatch && hasFinally) {
if (this.prev < entry.catchLoc) {
return handle(entry.catchLoc, true);
} else if (this.prev < entry.finallyLoc) {
return handle(entry.finallyLoc);
}
} else if (hasCatch) {
// 主要介绍这里 当前执行的case 小于catch代码所在的位置说明在try里面
if (this.prev < entry.catchLoc) {
return handle(entry.catchLoc, true);
}
} else if (hasFinally) {
if (this.prev < entry.finallyLoc) {
return handle(entry.finallyLoc);
}
} else {
throw new Error("try statement without catch or finally");
}
}
}
}
6. 最后介绍下 全局状态 Context
context构造函数和他原型上的方法~~
function Context(tryLocsList) {
// 初始化一个记录错误的数组
// tryLoc 是try所在的case catchLoc是catch所在代码的case
this.tryEntries = [{ tryLoc: "root" }];
// 上面的案例传入tryLocsList[[3,10]]会遍历这个数据把值复制到 tryEntries中
tryLocsList.forEach(pushTryEntry, this);
// 所以上面最后初始化后tryEntries=[{ tryLoc: "root",completion:{type:'normal'} },{tryLoc:3,catchLoc:10,completion:{type:'normal'}}]
this.reset(true); // 初始化
//初始化生成
/*
const res = {
prev: 0,
next: 0,
sent: undefined, // 发送
_sent: undefined,
done: false,
delegate: null, // 代表
method: "next",
arg: undefined,
tryEntries: [
{ tryLoc: "root", completion: { type: "normal" } },
{ tryLoc: 7, catchLoc: 14, completion: { type: "normal" } },
],
reset: Function,
};
*/
}
Context.prototype = {
constructor: Context,
reset: function (skipTempReset) {
// 初始化方法 初始化一系列的 默认值
this.prev = 0; // 当前执行的位置
this.next = 0; // 下一次执行的位置
// Resetting context._sent for legacy support of Babel's
// function.sent implementation.
this.sent = this._sent = undefined; //next传参
this.done = false; // 结束状态
this.delegate = null;
this.method = "next";
this.arg = undefined;
// 给对象出事话 complettion:{type: 'normal'}
this.tryEntries.forEach(resetTryEntry);
},
stop: function () {
// 停止方法 在switch case的最后执行
// 改变done为true, 并输出rval return的返回值
this.done = true;
var rootEntry = this.tryEntries[0];
var rootRecord = rootEntry.completion;
if (rootRecord.type === "throw") {
// 如果第一个状态未throw说明 报错没有被捕获直接抛出错误
throw rootRecord.arg;
}
return this.rval;
},
dispatchException: function (exception) {
//看上一
},
abrupt: function (type, arg) {
for (var i = this.tryEntries.length - 1; i >= 0; --i) {
var entry = this.tryEntries[i];
if (
entry.tryLoc <= this.prev &&
hasOwn.call(entry, "finallyLoc") &&
this.prev < entry.finallyLoc
) {
var finallyEntry = entry;
break;
}
}
if (
finallyEntry &&
(type === "break" || type === "continue") &&
finallyEntry.tryLoc <= arg &&
arg <= finallyEntry.finallyLoc
) {
// Ignore the finally entry if control is not jumping to a
// location outside the try/catch block.
finallyEntry = null;
}
// 主要看这部分 创建一个 {type:return,arg:报错返回值}
var record = finallyEntry ? finallyEntry.completion : {};
record.type = type;
record.arg = arg;
if (finallyEntry) {
this.method = "next";
this.next = finallyEntry.finallyLoc;
return ContinueSentinel;
}
return this.complete(record);
},
complete: function (record, afterLoc) {
//record {type:return,arg:报错返回值}
if (record.type === "throw") {
throw record.arg;
}
if (record.type === "break" || record.type === "continue") {
this.next = record.arg;
} else if (record.type === "return") {
// 主要看这里 返回值赋值给 context.rval 改变方法为return 改变next为end
this.rval = this.arg = record.arg;
this.method = "return";
this.next = "end";
} else if (record.type === "normal" && afterLoc) {
this.next = afterLoc;
}
// 返回ContinueSentinel .return .throw方法直接走下一个case
return ContinueSentinel;
},
catch: function (tryLoc) {
// 找到对应错误项 并返回
for (var i = this.tryEntries.length - 1; i >= 0; --i) {
var entry = this.tryEntries[i];
if (entry.tryLoc === tryLoc) {
var record = entry.completion;
if (record.type === "throw") {
var thrown = record.arg;
resetTryEntry(entry);
}
return thrown;
}
}
// The context.catch method must only be called with a location
// argument that corresponds to a known catch block.
throw new Error("illegal catch attempt");
},
};
over~
