JavaScript loop/Select structure

Like other languages, JavaScript has a looping structure and a selection structure.

Select structure:

1. if (condition) {
      //EXECUTE statement that satisfies the condition
   
2. if (condition) {
      //EXECUTE statement that satisfies the condition
   } else {
       ; Execute statement without condition
   }
3. if (condition 1) {
      //EXECUTE statement that satisfies condition 1
   } else if (condition 2) {
      //Meet Condition 2: N.. The EXECUTE statement
   } else{
      //EXECUTE statement that does not meet the above conditions
   }
4. switch (condition) {     Case matching result 1:
          //Match successful execution statement
         & nbsp break;   //exit switch
       Case matching result 2:
          //Match Successful execution statement
   & nbsp;       break;
       ....
       default:   //The above conditions are not successful
          //above conditions match unsuccessful execution statement
   }

Loop structure:

2. For (initial value; number of cycles; self-increment (self-decrement)) {
   Loop body
   }
   

   <script type= "Text/javascript" >for (var i=0;i<10;i++) {   document.write (i + "&nbsp;");  Output results: 0 1 2 3 4 5 6 7 8 9}</script>

4. for-in loops, primarily for loop arrays, but not commonly used, because this outputs hidden properties
   Specific Use method:
   

   <script type= "Text/javascript" >var array = [1,2,3,4,5,6];var i = 0;for (i in array) {  document.write (Array[i] + ' &nbsp; ');  i++;} Output is 1 2 3 4 5 6 </script>

   
   

   
   

   The traversal of an array mainly uses a for loop instead of using the for
6. While loop
   

   <script type= "Text/javascript" >var array = [1,2,3,4,5,6];var i = 0;while (i<array.length) {  document.write (Array[i] + ' &nbsp; ');  i++;} Output is 1 2 3 4 5 6 </script>

8. Do...while Cycle
   

   <script type= "Text/javascript" >var array = [1,2,3,4,5,6];var i = 0;do{  document.write (array[i] + ' &nbsp; ');  i++;} while (i<0);//output result is 1</script>

The difference between the for traversal array and the for-in traversal array

1. An array's traversal can only be an indexed array
2. the For loop will only iterate through the elements in the array, and for in will traverse the other properties
   Such as:

   <script type= "Text/javascript" >var array = [1,2,3,4,5,6];array.name = ' Zhang San '; for (var i = 0;i<array.length;i++) { C4/>document.write (array[i]+ ' &nbsp; ');} 1 2 3 4 5 6document.write (' <br/> '); var i=0;for (i in array) {  document.write (array[i]+ ' &nbsp; ');  i++;} 1 2 3 4 5 6 Zhang San </script>

   
   

   
   

The difference between a while loop and a do...while loop

1. The while loop is not looped if the condition is not satisfied
2. The Do...while loop is that if the condition is not met, it will still be executed once, as shown in the example above, the initial value of I is 0, does not satisfy the i<0 condition, but still outputs a value

JavaScript loop/Select structure