遇见对的人

<script>

let arr = [1, 2, 3, 4, 5, 6]

let arr1 = [1, 2, 3, 4, 5, 6]

let str = '1223423423423'

let str1 = '1223423423423'

console.log(arr.splice(1, 0, 'we')) //后面是长度 改变原数组 //增删改查

//[]

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console.log(arr)

//[1, "we", 2, 3, 4, 5, 6]

console.log(arr1.slice(1, 3)) //后面是下标 不会改变原数组

//[2, 3]

console.log(arr1)

//[1, 2, 3, 4, 5, 6]

console.log(str.substr(1, 3)) //后面是长度 不会改变原字符串

//223

console.log(str)

//1223423423423

console.log(str1.substring(1, 3)) //后面是下标 不会改变原字符串

//22

console.log(str1)

//1223423423423

console.log(NaN == NaN) //false

console.log(NaN === NaN) //false

console.log(undefined == undefined) //true

console.log(undefined === undefined) //true

console.log(null == null) //true

console.log(null === null) //true

 

var a = 'hello world';

var b = [];

var c = function () { };

console.log(a instanceof Object) //false

console.log(b instanceof Object) //true

console.log(c instanceof Object) //true

console.log(a instanceof Array) //false

console.log(b instanceof Array) //true

console.log(c instanceof Array) //false

console.log(a instanceof Function) //false

console.log(b instanceof Function) //false

console.log(c instanceof Function) //true

console.log(Object.prototype.toString.call(a))

console.log(Object.prototype.toString.call(b))

console.log(Object.prototype.toString.call(c))

console.log(Object.prototype.toString.call(null))

console.log(Object.prototype.toString.call(NaN))

console.log(Object.prototype.toString.call(undefined))

// 输出：

// [object String]

// [object Array]

// [object Function]

// [object Null]

// [object Number]

// [object Undefined]

 

</script>