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Reduction of type

2022-07-18 13:43:00 【To be a woman of light】

1.typeOf


//1.typeof  The type of 
type IDType=number |string
function printID(id:IDType){
    if(typeof id==="string"){ // If id The type of is a string  when 
        console.log(id.toLowerCase())
    }else{
        console.log(id)
    }
}

2. The type of equality is reduced （=== ==！！=）

3.instanceof Is an example of a certain type

// When judging whether the object is an instance ,
function printTime(time:string|Date) {
if(time instanceof Date){
// When time yes  Date  The type of time , Can be converted into 
console.log(time.toISOString())
}else{
  console.log(time.toUpperCase())
}

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