须知：每道题的完成时间最多1分钟。请自觉按照时间记录答案。
下面一共有18道前端题目，每道题目限时1分钟（其实大部分题目限时少于1分钟），答对12道以上的同学视为优秀。
下面的题目为全英文题目，但是也只需要小学英语知识就足够了。
话不多说，直接开始吧~
1. What is one function you can use to determine whether a value is an illegal number or not?
A: NaN()
B: isNaN()
C: isNumber()
D: parseFloat()
2. The following function never prints "bar" to the console, despite what is passed into the function. Why?
function foo(x) {
if (x = undefined) {
console.log('foo');
} else if (x == false) {
console.log('bar');
} else {
console.log('baz');
}
}
A: The first condition expression overwrites x.
B: The second condition expression overwrites x.
C: x can never be false because it's a function argument.
D: The first condition expression handles everything that the second would.
3. What primitive type is the variable result?
const result = NaN
A: Number
B: Boolean
C: Symbol
D: String
4. After the following code is executed, what is printed to the console?
function list() {
return [].slice.call(arguments);
}
var leadingThirtysevenList = list.bind(null, 37);
var list2 = leadingThirtysevenList();
console.log(list2);
A: null
B: [37]
C: []
D: undefined
5. How would you instantiate an object for the date January 2, 2000?
A: let d = new Date(); the internal representation of a date is the number of milliseconds since January 2, 2000
B: let d = new Date(1, 2, 2000);
C: let d = new Date(2000, 2, 1);
D: let d = new Date(2000, 0, 2);
6. Given the following:
console.log(iterator1.next().value); // ["0", "foo"]
Which snippet will set up iterator1 for the above behavior?
A: let map1 = new Map();const iterator1 = map1.entries();map1.set('0', 'foo');
B: let map1 = new Map();const iterator1 = map1.keys();map1.set('0', 'foo');
C: let map1 = Map();const iterator1 = map1.items();map1.set('0', 'foo');
D: let map1 = new Map();const iterator1 = map1.get();map1.set('0', 'foo');
7. What static method defines setters, getters, and other configurations for a new or existing property on an object?
A: Object["setProperty"]()
B: Object.prototype.Property()
C: Property.declare()
D: Object.defineProperty()
8. Given a complex object, foo, with keys that are not known ahead of time, how can you check if a given key, "k", is in the object without iterating through the whole object?
A: ...foo == k
B: foo contains k
C: "k" in foo
D: foo.apply(k)
9. Given that the sine of 90 degrees is 1, what is the result of the code below?let foo = Math.sin(90);
A: 1
B: A ReferenceError will be thrown; the trigonometry functions are meant to be called at a global scope:let foo = sin(90)
C: A ValueError will be thrown; Math.sin() expects a second argument specifying degrees or radians
D: Not 1, because Math.sin() expects the parameter to be in radians
10. What happens when an object inherits from another object using Object.create()?
A: A copy of the old object is created, and the constructor is used to construct the new object.
B: The prototype chain for the original object is given to the new object, giving a reference of and access to all of the original object properties.
C: One by one, the object's properties are copied over to the new object.
D: The new object is given a reference to the original object's constructor, which allows the new object to create a new prototype chain.
11. How can you remove all of the items within an array?
A: let arr = [‘hello’, ‘world’]; arr.length = 0;
B: var arr = [‘hello’, ‘world’]; arr.empty();
C: var arr = [‘hello’, ‘world’]; arr.remove(2);
D: var arr = [‘hello’, ‘world’]; arr.toShortList();
12. What is wrong with this snippet?
class MegaArray extends Array{
constructor(contents){
this.contents = contents;
}
}
let mArr = new MegaArray(1, 2, 3);
A: The class constructor does not call parent().
B: Classes both cannot inherit built-in types and must pass constructor arguments to the parent's constructor using super().
C: The class constructor does not call super(), so this is not defined when inheriting from Array.
D: Classes cannot inherit from built-in types.
13. Which code snippet correctly shows unpacking the arguments object into an array?
A: Array.toArray(arguments)
B: [arguments]
C: arguments.toArray()
D: Array.from(arguments)
14. The following snippet throws an error. Why?
function foo() {
'use strict';
(function () {
var point = {x: 42, y: 27};
with (point) {
console.log('The coordinates are: x: ', x, 'y: ', y);
}
})();
}
foo();
A: You cannot use immediately invoked function expressions (IIFEs) in strict mode
B: You cannot add the 'use strict'; directive in a function
C: You cannot declare object literals in strict mode
D: You cannot use with statements in strict mode
15. When inheriting from a parent class, what does the super keyword do in the child's constructor?
A: super invokes the parent's constructor, and by extension, defines the lexical context and this object for the child class.
B: super instantiates the parent class and deep copies the properties over to the child class.
C: super invokes the parent constructor, and then performs a deep copy of the parent properties over to the child class to make a wholly new object.
D: super instantiates the parent class and copies the properties over as virtual properties on the child class.
16. What does this print to the console and why?
function Foo() {}
function Bar() {}
Bar.prototype = Object.create(Foo.prototype);
let banana = new Bar();
let apple = new Foo();
console.log(Bar.prototype.isPrototypeOf(apple));
console.log(Bar.prototype.isPrototypeOf(banana));
console.log(Foo.prototype.isPrototypeOf(banana));
A: ReferenceError will be thrown
B: true, true, true
C: true, true, false
D: false, true, true
17. What is printed to the console in the following code snippet?
let foo = () => {
console.log("User1");
return false;
}
let bar = () => {
console.log("User2");
return true;
}
let x = false || bar() || foo();
A: undefined
B: User2 User1
C: User1 User2
D: User2
18. After the following code is executed, what is printed to the console?
let map1 = new Map();
map1.set('0', 'foo');
map1.set(1, 'bar');
const iterator1 = map1.entries();
console.log(iterator1.next().value);
A: "0"
B: "foo"
C: ["0", "foo"]
D: ["foo"]
各位同学，上面的题目怎么样是不是很简单啊~
下面公布答案：
BAABD ADCDB ACDDA DD
你答对了多少呢？
请按照时间要求，自觉答题，并把你的分数写在评论里吧~
欢迎讨论问题！
