「JavaScript」- 语法学习

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解决方案

for / forEach / for..of

// for

for (var b; b = a.pop(); ) {      // for 循环的特殊用法
    do_sth(b);
}

// forEach

[].forEach(function (item, index) {
	console.log(index + " " + item)
});

[].forEach(function (item, index) {
	it => console.log(it)
});

// for...of => does use an object-specific iterator and loops over the values generated by that.

const array1 = ['a', 'b', 'c'];
for (const element of array1) {
  console.log(element);
}

// for...in => loops over enumerable property names of an object.
 
const object = { a: 1, b: 2, c: 3 };
for (const property in object) {
  console.log(`${property}: ${object[property]}`);
}

async…await

async function – JavaScript | MDN
javascript – Using async/await with a forEach loop – Stack Overflow

通过 async 定义的函数,允许异步执行,而对该函数的调用使用 await 能够等待该异步函数执行结束。

function resolveAfter2Seconds() {
	return new Promise(resolve => {
		setTimeout(() => {
			resolve('resolved');
		}, 2000);
	});
}

async function asyncCall() {
	console.log('calling');
	const result = await resolveAfter2Seconds();
	console.log(result);
	// expected output: "resolved"
}

asyncCall();

注意事项,在 forEach 中传入 async 标注的函数是无效的,因为 forEach 会并行执行函数。

参考文献

declaration for variable in while condition in javascript – Stack Overflow
JavaScript Array forEach() Method
for…in – JavaScript | MDN
for…in – JavaScript | MDN
javascript – What is the difference between ( for… in ) and ( for… of ) statements? – Stack Overflow