Learn about parameter passing in javascript again

Parameters of all functions in javascript are passed by value. The following test is performed:

Function addTen (num) {num + = 10; return num;} var count = 20; var result = addTen (count); alert (cont ); // 20 alert (result); // 30

Okay, the above is just a transfer of the basic type. Let's take a look at the transfer of the reference type:

Function setName (obj) {obj. name = "Mark";} var person = new Object (); setName (person); alert (person. name); // Mark

This seems to be a reference transfer, not a value transfer, so let's test again:

Function setName (obj) {obj. name = "Mark"; obj = new Object (); obj. name = "David";} var person = new Object (); setName (person); alert (person. name); // Mark

The only difference between this example and the previous example is that two lines of code are added after the setName () function: one line of code re-defines an object for obj, another line of code defines a name attribute with different values for this object. After the persion is passed to the setName () function, its name attribute is set to Mark, a new object is assigned to obj, and its name attribute is set to David. If the person is passed by reference, the person will be automatically changed to a new object pointing to its name attribute value as David. However, when you access person. name again, the displayed value is still Mark. This indicates that the original reference remains unchanged even if the parameter value is modified within the function. In fact, when you override obj in a function, this variable references a local object. This local object will be destroyed after the function is executed.