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=: adsignatio operator.
==: Aequalitas operans. Cum species valoris in utraque parte signi aequalis diversae sint, convertentur ad idem genus primum, et tunc valores comparabuntur ut videant si sint aequales.
===: Strictioris operator, nulla species conversionis perficitur.
Solebant comparare an pares sint, uti ===.

//==做类型转换后判断
console.log("1" == true)//true
console.log(1 == true)//true

//===不做类型转换，类型不同则直接false
console.log(1 === true)//false
console.log("1" === "1")//true

//比较object, Array, Function时，比较他们是否指向同一个对象
let arr1 = [1,2,3]
let arr2 = arr1
console.log(arr1 === arr2)

//null和undefined
console.log(null == undefined)//true
console.log(null === undefined)//false
console.log(null === null)//true
console.log(undefined === undefined)//true
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