JavaScript例子

1.

console.log("ddd")

var data = [];
for(var i = 0 ; i < 3; i++){
    data[i]=function() {
        console.log(i);
    }
}

data[0]();// 3
data[1]();// 3
data[2]();// 3
console.log("-----------");
function counter() {
    var x = 0;
    
    return {
        increase: function increase() { return ++x; },
        decrease: function decrease() { return --x; }
    };
}

var ctor = counter();

console.log(ctor.increase());
console.log(ctor.decrease());

console.log(ctor.increase);
console.log(ctor.decrease);


console.log("-----------");

let a = 1, b = {c: 3};
a = 2;
var s={c: a} = b;
console.log(a);
console.log("-----------");

console.log(new Date("2021/10/15 15:00:12"));
console.log(new Date("2021-10-15 15:00:13"));
console.log("-----------");


function func() {
    console.time("func");
    var obj = {
        a: 1
    };
    for(var i = 0; i < 100000; i++)
    {
        obj.a=i;
    }
    console.timeEnd("func");
}
func();

function funcWith() {
    console.time("funcWith");
    var obj = {
        a: 1
    };
    with(obj) {
        for(var i = 0; i < 100000; i++) {
            a = i;
        }
    }
    console.timeEnd("funcWith");
}

funcWith();
console.log("-----------");

console.log(false.toString());
console.log(false);

console.log(5 + null)    // 返回 5         null 转换为 0
console.log("5" + null)  // 返回"5null"   null 转换为 "null"
console.log("5" + 1)     // 返回 "51"      1 转换为 "1" 
console.log("5" - 1)     // 返回 4         "5" 转换为 5

console.log("-----------");

var y = "5";      // y 是一个字符串
var x = 1 + y;  
console.log(x)
console.log("-----------");

var x = 0.1;
var y = 0.2;
var z = x + y;
if(z*10==30){
    console.log("yes")
}
console.log(z)
console.log("-----------");

websites = {site:"菜鸟教程", url:"www.runoob.com", like:460,}
var colors = [5, 6, 7,]; //这样数组的长度可能为3 也可能为4。
if (typeof myObj !== "undefined" && myObj !== null) 
// if (myObj !== null && typeof myObj !== "undefined") 

    console.log(colors.length)
    else
        console.log(colors.length+1)
console.log("-----------");

var obj = {
    birth: 1990,
    getAge: function (year) {
        var b = this.birth; // 1990
        var fn = (y) => y - this.birth; // this.birth仍是1990
        return fn.call({birth:2000}, year);
    }
};
var obj1={
    birth:2005
}
console.log(obj.getAge(2015)); // 25 ,fn.call({birth:2000}, year)传递的对象无用
console.log(obj.getAge.call(obj1,2015));//10 
console.log("__________")


var person1 = {
  firstName:"Johnrrr",
  lastName: "Doerrr",
  fullName: function() {
      var fn = () => this.firstName + " " + this.lastName;
    return fn.call();
  }
//  fullName: () => {return this.firstName + " " + this.lastName;}
  
}
var person2 = {
  firstName:"John",
  lastName: "Doe",
}
console.log(person1.fullName()) //Johnrrr Doerrr
console.log(person1.fullName.call(person2));  // 返回 "John Doe"

console.log("__________")

let tea = [1,2,{name:true}];
let arr4 = tea.map((it,id)=>{
    if (id===2) {
        it.name = 'edit'
    }
     return it
})

console.log(tea[2].name)