index.js
/**
js的数据类型有：
string, number, boolean, undefined, null, symbel
object, array, function
*/
console.log('-----------Undefined--------')
console.log(undefined == undefined) // true
console.log(undefined === undefined) // true
console.log()
console.log('-----------Null--------')
console.log(null == null) // true
console.log(null === null) // true
console.log()
console.log('-----------String--------')
console.log('name' == 'name') // true
console.log('name' === 'name') // true
console.log()
console.log('-----------Number--------')
console.log(10 == '10') // true
console.log(10 == '010') // true
console.log(10 === '10') // false
console.log(10 === 10) // true
console.log(NaN == NaN) // false
console.log(NaN === NaN) // false
console.log(isNaN(NaN)) // true
console.log()
console.log('-----------Boolean--------')
console.log(true == true) // true
console.log(true === true) // true
console.log('-----------Object--------')
console.log({} == {}) // false
console.log({} === {}) // false
console.log(typeof {}) // 'object'
console.log(typeof {} == 'object') // true
// console.log(Object.isObject({})) // true
console.log('-----------typeof的值（无法判断 object, array, null--------')
console.log(typeof '') // 'string'
console.log(typeof 0) // 'number' -------- 111
console.log(typeof true) // 'boolean'
console.log(typeof undefined) // 'undefined'
console.log(typeof null) // 'object' -------- 222
console.log(typeof NaN) // 'number' -------- 111
console.log(typeof {}) // object --------222
console.log(typeof []) // object --------222
console.log(typeof function () {}) // function
console.log('-----------Object.prototype.toString.call的值--------')
console.log(Object.prototype.toString.call('')) // '[object String]'
console.log(Object.prototype.toString.call(0)) // '[object Number]'
console.log(Object.prototype.toString.call(true)) // '[object Boolean]'
console.log(Object.prototype.toString.call(undefined)) // '[object Undefined]'
console.log(Object.prototype.toString.call(null)) // '[object Null]'
console.log(Object.prototype.toString.call(NaN)) // '[object Number]'
console.log(Object.prototype.toString.call({})) // '[object Object]'
console.log(Object.prototype.toString.call([])) // '[object Array]'
console.log(Object.prototype.toString.call(new Function ())) // '[object Function]'
console.log(Object.prototype.toString.call(function (){})) // '[object Function]'
console.log('-----------if 条件判断--------')
if (0) { // 非空判断
console.log(' if (0) ==> true ')
} else {
console.log(' if (0) ==> false ') // false
}
if ('0') {
console.log(' if ("0") ==> true ') // true
} else {
console.log(' if ("0") ==> false ')
}
if (undefined) {
console.log(' if (undefined) ==> true ')
} else {
console.log(' if (undefined) ==> false ') // false
}
if (null) {
console.log(' if (null) ==> true ')
} else {
console.log(' if (null) ==> false ') // false
}
if ({}) {
console.log(' if ({}) ==> true ') // true
} else {
console.log(' if ({}) ==> false ')
}
if ([]) {
console.log(' if ([]) ==> true ') // true
} else {
console.log(' if ([]) ==> false ')
}
if (new Function()) {
console.log(' if (new Function()) ==> true ') // true
} else {
console.log(' if (new Function()) ==> false ')
}
/**
-----------if 条件判断--------
if (0) ==> false
if ("0") ==> true
if (undefined) ==> false
if (null) ==> false
if ({}) ==> true
if ([]) ==> true
if (new Function()) ==> true
*/
