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x !== x 返回 true
js
const x = ? // Please fill in the value of "x?
if (x !== x) {
console.log('hello fatfish')
}如果你有仔细阅读 es6 的教程的话，就知道这个问题是一个典型的 demo
js
const x = NaN // Please fill in the value of "x?
if (x !== x) {
console.log('hello fatfish')
}
console.log(NaN === NaN) // false
console.log(x !== x) // true
console.log(Number.isNaN(x)) // true(!isNan(x) && x !== x) 返回 true
现在难度提高
js
const x = ? // Please fill in the value of "x?
if(!isNaN(x) && x !== x) {
console.log('hello fatfish')
}你知道 Object.defineProperty() 吗？
请参考 Object.defineProperty() - JavaScript | MDN
js
window.x = 0 // Any value is OK
Object.defineProperty(window, 'x', {
get () {
return Math.random()
}
})
console.log(x) // 0.12259077808826002
console.log(x === x) // false
console.log(x !== x) // true如何使得 x === x+1
使用极大值 Number.MAX_SAFE_INTERGER
参考 Number.MAX_SAFE_INTEGER - JavaScript | MDN
js
const x = Number.MAX_SAFE_INTEGER + 1// Please fill in the value of "x?
if (x === x + 1) {
console.log('hello fatfish')
}如何使得 x > x
使用 Symbol.toPrimitive
js
const x = { // Please fill in the value of "x?
value: 1,
[ Symbol.toPrimitive ] () {
console.log('x', this.value)
return --this.value
}
}
if (x > x) {
console.log('hello fatfish')
}实现 typeof x === 'undefined' && x.length > 0
答案是 document.all()
js
const x = document.all // Please fill in the value of "x?
if(typeof x === 'undefined' && x.length > 0) {
console.log('hello fatfish')
}
console.log(x)
console.log(typeof x)
console.log(x === undefined)参考 javascript - Why is document.all falsy? - Stack Overflow
贡献者
jiechen