2-13-数组的运用

一、some循环

平常使用的forEach是无法使用break和return中断的，如果想要强行让它中断，就需要抛出错误：

var BreakException = {};

try {

[1, 2, 3].forEach(function(el) {

console.log(el);

if (el === 2) throw BreakException;

});

} catch (e) {

if (e !== BreakException) throw e;

}

初次之外，我们还可以使用some

arr.some((item, index) => {

console.log('arr');

if (item == '苏大强') {

console.log(index);

return true;

}

});

二、every

判断数组中的state，如果为真则保留下来：

``
const arr = [

{ id: 1, name: ‘西瓜’, state: true },

{ id: 2, name: ‘榴莲’, state: false },

{ id: 3, name: ‘草莓’, state: true }

]

const result = arr.every(item => item.state);

console.log(result);

## 三、reduce

把数组中所有水果总价累加起来

const arr = [

{ id: 1, name: ‘西瓜’, state: true, price: 80, count: 1 },

{ id: 2, name: ‘榴莲’, state: false, price: 70, count: 2 },

{ id: 3, name: ‘草莓’, state: true, price: 60, count: 3 }

]

**第一种写法是：**

let amt = 0;

arr.filter(item => item.state).forEach(item => {

amt += item.price * item.count;

});

**第二种写法是：**

// reduce((‘累加的结果’, ‘当前项’) => { }, 初始值)

const result = arr.filter(item => item.state).reduce((amt, item) => {

return amt += item.price * item.count;

}, 0);

**简化写法：**

const result = arr.filter(item => item.state).reduce((amt, item) => amt
+= item.price * item.count, 0);