1. Why does the following code print 6 6’s

Example 1:let i = 0
for(i = 0; i<6; i++){
  setTimeout(() = >{
    console.log(i)
  },0)}Copy the code

SetTimeout () is asynchronous code that executes after synchronous code has finished executing. After the for loop completes, there are six console.log(I) tasks in the queue, and the scope is I = 6 (there is only one I, not the nearest rule), so it prints six sixes.

2. Method of printing 0, 1, 2, 3, 4, 5

Example 2:for(let i = 0; i<6; i++){
setTimeout(() = >{
console.log(i)
},0)}Copy the code

According to the ES6 standard, every time the for loop is executed, I is copied, so there will be six I after setTimeout(), and then print 0, 1, 2, 3, 4, 5.

3. Other methods of printing 0, 1, 2, 3, 4, 5

Example 3: Closureslet i 
for(i = 0; i<6; i++){
  !function(j){
      setTimeout(() = >{
        console.log(j)
      },0)
  }(i)
}
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Fact 4: Array pushvar arr4 = [];
var  n = 0;
for(var i = 0; i<6; i++) { n+=1;
arr4.push(n-1)}console.log(arr4)
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Example 5: UsesetTimeoutThe third argument to, pass in Ilet i
for(i = 0; i<6; i++){
    setTimeout((value) = >{
      console.log(value)
    },0,i)
}
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Example 6: UtilizationconstThe keywordlet i
for(i = 0; i<6; i++){
  const x = i
  setTimeout(() = >{
    console.log(x)    
  })
}
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