js中的类型判断

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 

*/