ECMAScript新语法,统称ECMA-262
表达式和运算符
可选链操作符(Optional Chaining)
语法
obj?.prop
obj?.[expr]
arr?.[index]
func?.(args)
示例
const adventurer = {
name: 'Alice',
cat: {
name: 'Dinah'
}
};
const dogName = adventurer.dog?.name;
console.log(dogName);
// expected output: undefined
console.log(adventurer.someNonExistentMethod?.());
// expected output: undefined
空值合并运算符(Nullish coalescing Operator)
语法
leftExpr ?? rightExpr
示例
const foo = null ?? 'default string';
console.log(foo); // expected output: "default string"
const bar = undefined ?? 'default string';
console.log(bar); // expected output: "default string"
const baz = 0 ?? 42;
console.log(baz); // expected output: 0
const qux = '' ?? 42;
console.log(qux); // expected output: ''
