2019/9/5 第三部分：?级篇 | FE-Interview JS Object null undefined boolea number string symbol JS IEEE 754 NaN NaN number let a = 111 // a.toString() // number Object let a = { name: FE } let b = a b.name = EF console.log(a.name) // EF typeof null typeof 1 // number typeof 1 // string blog.poetries.top/FE-Interview-Questions/advance/#?、javascript进阶 1/105 2019/9/5 第三部分：?级篇 | FE-Interview typeof undefined // undefined typeof true // boolean typeof Symbol() // symbol typeof b // b undefined object typeof typeof [] // object typeof {} // object typeof console.log // function null Bug object typeof null // object JS 32 000 null object Bug Object.prototype.toString.call(xx) [object Type] let a // undefined a === undefined // undefined let undefined = 1 // // // void // undefined a === void 0 blog.poetries.top/FE-Interview-Questions/advance/#?、javascript进阶 2/105 2019/9/5 第三部分：?级篇 | FE-Interview undefined null false NaN 0 -0 true valueOf toString let a = { valueOf() { return 0 } } 1 + 1 // 11 2 * 2 // 4 [1, 2] + [2, 1] // 1,22,1 // [1, 2].toString() -> 1,2 // [2, 1].toString() -> 2,1 // 1,2 + 2,1 = 1,22,1 a + + b blog.poetries.top/FE-Interview-Questions/advance/#?、javascript进阶 3/105 2019/9/5 第三部分：?级篇 | FE-Interview a + + b // -> "aNaN" // + b -> NaN // + 1 -> 1 [] == ![] // -> true true // [] true [] == false false // 8 [] == ToNumber(false) [] == 0 // 10 ToPrimitive([]) == 0 // [].toString() -> == 0 // 6 0 == 0 // -> true toPrimitive unicode bl