Reference pass of JavaScript object parameters

Today I encountered a problem, how to affect parameter changes to the outside of the function, such as:

<script>
  var myname = "wood";
  A(myname);
  (myname);

  function A(n) {
    n = "Yao";
  }
</script>

The output result is still wood, which means that when myname is passed into function A, it is equivalent to a copy of myname in the function body. The value of this copy is equal to myname, and the operations performed on it in the function body are performed on this copy.

But the situation is different. When the passed parameters are arrays or objects, the changes made to the parameters in the function body will be reflected on the original variable.

<script>
  var myname = ["wood"];
  A(myname);
  (myname[0]);

  function A(n) {
    n[0] = "Yao";
  }
</script>

It can be seen that the first element of the friut array has been changed in the above code.

Here is an example of an object:

<script>
  var myname = {name1:"wood"};
  A(myname);
  (myname.name1);

  function A(n) {
    n.name1 = "Yao";
  }
</script>

It can be clearly seen that the changes in the parameters in the function body affect the original variable, which is qualitatively different from the usual transmission parameters. Special attention is required.

But, when assigning values ​​to an incoming array or object within the function body, this change will not be reflected in the original variable outside the function body!

Please see:

<script>
  var myname = {name1:"wood"};
  A(myname);
  (myname.name1);

  function A(n) {
    n = {name1:"Yao"};
  }
</script>

According to the theory that the changes inside the function above will be reflected in the original variable, you must think that the value of the name1 attribute of the myname variable has become 'Yao' after executing A(). But the result is a bit unacceptable.

The reason is that when using assignment operations in the function body, the system creates a variable named p. This p is a variable inside the function, and assigning it to the value only works in the function body. The outside myname is still the original myname.

The only difference between this step and the original code operation is whether to assign a new value to the parameter in the function body or to change the attributes or elements of the array.

Below we reimplement an example of clock digital formatting output using the method of passing objects:

<script>
  var mytime = (function() {
    getTime();
  }, 1000);
  //alert("ok");
  function getTime() {
    var timer = new Date();
    var t = {
        h: (),
        m: (),
        s: ()
      }
      //Pass the time object t into the function checkTime(), and directly change the value in the object in checkTime().      // without receiving the return value and assigning the value again    checkTime(t);
    ("timer").innerHTML =  + ":" +  + ":" + ;
  }

  function checkTime(i) {
    if ( < 10) {
       = "0" + ;
    }
    if ( < 10) {
       = "0" + ;
    }
    if ( < 10) {
       = "0" + ;
    }
  }
</script>

Examples: Use the setInterval() function to call refresh events regularly, or you can also use setTimeout() to call recursively in getTime().

The above is all about this article, I hope it will be helpful for everyone to learn JavaScript programming.