//  1.入门版本   var arr1 = [9,7,4,5,6];   for(var j = 0; j < arr1.length-1; j++) {
      for(var i = 0; i < arr1.length-1; i++){
        if(arr1[i] > arr1[i+1]){
          var temp = arr1[i];         arr1[i]=arr1[i+1];         arr1[i+1] = temp;       }     }   }   console.log(arr1);

//  2.升级版 var arr1 = [9,7,4,5,6];  for(var j = 0; j < arr1.length-1; j++) {
      for(var i = 0; i < arr1.length-1-i; i++){
        if(arr1[i] > arr1[i+1]){
        　　var temp = arr1[i];       　　arr1[i]=arr1[i+1];       　　arr1[i+1] = temp;       }     }  }  console.log(arr1);

//  3.终极版 var arr1 = [9,7,4,5,6];  for(var j = 0; j < arr1.length-1; j++) {
     var flag = true;    for(var i = 0; i < arr1.length-1; i++){
        if(arr1[i] > arr1[i+1]){
          var temp = arr1[i];         arr1[i]=arr1[i+1];         arr1[i+1] = temp;         flag = false;       }     }    if(flag) {
       break;    }  }  console.log(arr1);