JavaScript常用使用_03
JavaScript常用使用_03
JavaScript常用使用_03

判断空对象

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function checkObj(obj) {
    return Object.keys(obj).length === 0;
}
checkObj([]); // true
checkObj({}); // true
//-------------------------------------------


Object.keys({}).length; // 长度为0
Object.keys({foo: "bar"}).length; // 长度为1

Object.keys([]).length; // 长度为0
Object.keys(["fei"]).length; // 长度为1

常见加密解密

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// Base64的编码与解码
let foo = "Hello fei";
window.btoa(foo); // SGVsbG8gZmVp
window.atob("SGVsbG8gZmVp"); // Hello fei

//  url 编码解码
let url = "http://github.com/search?name=1 2 3 $age=456";
encodeURI(url); // http://github.com/search?name=1%202%203%20$age=456
decodeURI("http://github.com/search?name=1%202%203%20$age=456");

// url 中参数编码解码
let bar = "a=123&b=456";
encodeURIComponent(bar); // a%3D123%26b%3D456
decodeURIComponent("a%3D123%26b%3D456"); // a=123&b=456

Blob 和 String相互转换

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// 将String字符串转换成Blob对象
var blob = new Blob(['daFei'], {
    type: 'text/plain'
});
console.log(blob);

//将Blob 对象转换成字符串
var reader = new FileReader();
reader.readAsText(blob, 'utf-8');
reader.onload = function (e) {
    console.info(reader.result);
}

参数

解构参数 和 方法参数

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// 解构参数
function foo({name = "daFei", age = 18}={}) {
    console.log(name,age);
}
foo({name:"foo",age:20});
foo({age:22});

// 方法参数
function bar(name="daFei",callBack) {
    if (callBack) {
        callBack();
    }else{
        console.log("没有执行");
    }
}
bar("bar", () => {
    console.log("开始执行");
});
bar("bar2")

判断浏览器类型

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// Browser environment sniffing
var inBrowser = typeof window !== 'undefined';
var inWeex = typeof WXEnvironment !== 'undefined' && !!WXEnvironment.platform;
var weexPlatform = inWeex && WXEnvironment.platform.toLowerCase();
var UA = inBrowser && window.navigator.userAgent.toLowerCase();
var isIE = UA && /msie|trident/.test(UA);
var isIE9 = UA && UA.indexOf('msie 9.0') > 0;
var isEdge = UA && UA.indexOf('edge/') > 0;
var isAndroid = (UA && UA.indexOf('android') > 0) || (weexPlatform === 'android');
var isIOS = (UA && /iphone|ipad|ipod|ios/.test(UA)) || (weexPlatform === 'ios');
var isChrome = UA && /chrome\/\d+/.test(UA) && !isEdge;
var isPhantomJS = UA && /phantomjs/.test(UA);
var isFF = UA && UA.match(/firefox\/(\d+)/);

抛出异常

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try {
  throw  "抛出异常";
} catch (err) {
  console.error("捕获___" + err);
}

解构重命名

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const {fei: fei_temp, foo: foo_temp} = {fei: "123", foo: "helloWorld"};
console.log(fei_temp, foo_temp); // 对 fei 和 foo 重新定义名字

剩余

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let {a, b, ...fei} = {a: 10, b: 20, c: 30, d: 40};

默认

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let {foo, b = 5} = {foo: 3};
let {foo, b: bb = 5} = {foo: 3};

demo

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<script>
  let foo = [];
  let bar = [];
  let fei = [];

  const testFun = () => {
    let foo = [1, 2, 3];
    let bar = ['a', 'b', 'c'];
    let fei = ['hello', 'world'];
    return {foo, bar, fei}
  }

  try {
    ({foo, bar, fei} = testFun())
  } catch (e) {
    ({foo, bar, fei} = testFun())
  }

  console.log(foo, bar, fei)
</script>

高阶函数 filter map reduce

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// 高阶函数 filter map reduce  用es6语法
// 过滤小于20的值,返回布尔值 true 或者 false
// 循环数组中的每一个元素
//接受一个函数作为参数，这个函数作为一个累加器，从左到右遍历整个类型数组，最后返回一个单一的值
const nums = [10, 15, 18, 25, 34];
let newNums = nums.filter(item => item < 20) 
.map(item2 => item2 * 2) 
.reduce((total, item3) => total + item3); 

//--------------------
const nums = [10, 15, 18, 25, 34];
let newNum_1 = nums.filter(function (item1) {
    return item1 < 20;
});
console.log(newNum_1); // [10, 15, 18]

let newNum_2 = newNum_1.map(function (item2) {
    return item2 * 2;
});
console.log(newNum_2); // [20, 30, 36]

let newNum_3 = newNum_2.reduce(function (total, item3) {
    return total + item3;
})
console.log(newNum_3); // 86

map 妙用

转换数组中类型

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// 字符数组转数字数组
let strArr = ["1", "2", "3"];
let numArr = strArr.map(Number)
console.log(numArr)

// number数组转为string数组
let numArr1 = [1, 2, 3]
let strArr1 = numArr1.map(String)

console.log(strArr1)

filter 双重循环去重

场景,对个一个数组去重,条件是根据另一个数组中的数据

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// filter中 双重循环去重
const words1 = ['fei', 'foo', 'bar']; // 实际场景为对象数组
const words2 = ['fei'];
let newArr = words1.filter(item => {
    const found = words2.findIndex(row => item === row)
    if (found === -1) { // 没有找到,说明当前值唯一
        return true;
    }
})
console.log(newArr); // 输出 ['foo', 'bar']

set 和 map

set 利用唯一,数组去重

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[...new Set([1, 1, 2, 2, 5, 7])]

获取当前之后的时间

JavaScript获取当前时间减去10分钟

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// JavaScript获取当前时间减去10分钟
function dateDecrease(dStr,interval = 10) {
    let d = new Date(
        dStr.substring(0, 4),
        dStr.substring(5, 7) - 1,
        dStr.substring(8, 10),
        dStr.substring(11, 13),
        dStr.substring(14, 16),
        dStr.substring(17, 19)
    );
    d.setTime(d.getTime() - interval * 60 * 1000);
    //小于10前面补0
    let getMonth = (d.getMonth() + 1) < 10 ? "0" + (d.getMonth() + 1) : d.getMonth() + 1;
    let getDate = d.getDate() < 10 ? "0" + (d.getDate()) : d.getDate();
    let getHours = d.getHours() < 10 ? "0" + (d.getHours()) : d.getHours();
    let getMinutes = d.getMinutes() < 10 ? "0" + (d.getMinutes()) : d.getMinutes();
    return d.getFullYear() + "-" + getMonth + "-" + getDate + " " + getHours + ":" + getMinutes;
}
console.log(dateDecrease('2022-02-04 08:00'))

JavaScript获取当前时间加上10分钟

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// JavaScript获取当前时间加上10分钟
function dateAdd(dStr, interval = 10) {
    let d = new Date(
        dStr.substring(0, 4),
        dStr.substring(5, 7) - 1,
        dStr.substring(8, 10),
        dStr.substring(11, 13),
        dStr.substring(14, 16),
        dStr.substring(17, 19)
    );
    d.setTime(d.getTime() + interval * 60 * 1000);
    //小于10前面补0
    let getMonth = (d.getMonth() + 1) < 10 ? "0" + (d.getMonth() + 1) : d.getMonth() + 1;
    let getDate = d.getDate() < 10 ? "0" + (d.getDate()) : d.getDate();
    let getHours = d.getHours() < 10 ? "0" + (d.getHours()) : d.getHours();
    let getMinutes = d.getMinutes() < 10 ? "0" + (d.getMinutes()) : d.getMinutes();
    return d.getFullYear() + "-" + getMonth + "-" + getDate + " " + getHours + ":" + getMinutes;
}
console.log(dateAdd('2022-02-20 08:00'))

获取当天时间戳

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//**** 单位都是毫秒

// 当天00点00分00秒 时间戳 1659974400000
new Date(new Date().toLocaleDateString()).getTime()

// 当天23点59分59秒 时间戳 1660060799999
new Date(new Date().toLocaleDateString()).getTime() + 24 * 60 * 60 * 1000 - 1

// 当前时间戳 1659976187168
new Date().getTime()

// 当前日期 '2022/8/9'
new Date().toLocaleDateString()

// 当前时间 '2022/8/9 00:29:14'
new Date().toLocaleString()