js数组对象中的操作
2019-08-09 本文已影响0人
糖醋里脊120625
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>vue自定义过滤器</title>
<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1,maximum-scale=1,user-scalable=no" />
</head>
<body>
<div class="test">
</div>
<script type="text/javascript">
//对象操作
let meals = {
mealA: 'Breakfast',
mealB: 'Lunch',
mealC: 'Dinner'
};
for(let key of Object.keys(meals)) {
let mealName = meals[key];
// ... do something with mealName
console.log(mealName);
}
//对象操作
let simpleColors = {
colorA: 'white',
colorB: 'black'
};
let natureColors = {
colorC: 'green',
colorD: 'yellow'
};
Object.setPrototypeOf(natureColors, simpleColors);
Object.keys(natureColors); // => ['colorC', 'colorD']
natureColors['colorA']; // => 'white'
natureColors['colorB']; // => 'black'
//函数式
// 简单的缓存工具
// 匿名函数创造了一个闭包
const cache = (function() {
const store = {};
return {
get(key) {
return store[key];
},
set(key, val) {
store[key] = val;
}
}
}());
console.log(cache) //{get: ƒ, set: ƒ}
cache.set('a', 1);
cache.get('a'); // 1
//不是高阶函数
////map()
//map() 方法创建一个新数组，其结果是该数组中的每个元素都调用一个提供的函数后返回的结果。map 不会改变原数组
var animals = [
{ name: "Fluffykins", species: "rabbit" },
{ name: "Caro", species: "dog" },
{ name: "Hamilton", species: "dog" },
{ name: "Harold", species: "fish" },
{ name: "Ursula", species: "cat" },
{ name: "Jimmy", species: "fish" }
];
var names = [];
for (let i = 0; i < animals.length; i++) {
names.push(animals[i].name);
}
console.log(names); //["Fluffykins", "Caro", "Hamilton", "Harold", "Ursula", "Jimmy"]
//高阶函数
var animals = [
{ name: "Fluffykins", species: "rabbit" },
{ name: "Caro", species: "dog" },
{ name: "Hamilton", species: "dog" },
{ name: "Harold", species: "fish" },
{ name: "Ursula", species: "cat" },
{ name: "Jimmy", species: "fish" }
];
var names = animals.map(x=>x.name);
console.log(names); //["Fluffykins", "Caro", "Hamilton", "Harold", "Ursula", "Jimmy"]
// 不使用高阶函数
//filter() 方法会创建一个新数组，其中包含所有通过回调函数测试的元素。
//filter 为数组中的每个元素调用一次 callback 函数， callback 函数返回 true 表示该元素通过测试，保留该元素，false 则不保留。filter 不会改变原数组，它返回过滤后的新数组。
var animals = [
{ name: "Fluffykins", species: "rabbit" },
{ name: "Caro", species: "dog" },
{ name: "Hamilton", species: "dog" },
{ name: "Harold", species: "fish" },
{ name: "Ursula", species: "cat" },
{ name: "Jimmy", species: "fish" }
];
var dogs = [];
for (var i = 0; i < animals.length; i++) {
if (animals[i].species === "dog") dogs.push(animals[i]);
}
console.log(dogs);
//使用高阶函数filter
var animals = [
{ name: "Fluffykins", species: "rabbit" },
{ name: "Caro", species: "dog" },
{ name: "Hamilton", species: "dog" },
{ name: "Harold", species: "fish" },
{ name: "Ursula", species: "cat" },
{ name: "Jimmy", species: "fish" }
];
var dogs = animals.filter(x => x.species === "dog");
console.log(dogs); // {name: "Caro", species: "dog"}
// 不使用高阶函数
//reduce
//reduce 方法对调用数组的每个元素执行回调函数，最后生成一个单一的值并返回。 reduce 方法接受两个参数：1）reducer 函数（回调），2）一个可选的 initialValue。
const arr = [5, 7, 1, 8, 4];
let sum = 0;
for (let i = 0; i < arr.length; i++) {
sum = sum + arr[i];
}
console.log(sum);//25
// 使用高阶函数
const arr = [5, 7, 1, 8, 4];
const sum = arr.reduce((accumulator, currentValue) => accumulator + currentValue,0);
console.log(sum)//25
</script>
</body>
</html>
