In JavaScript, when an associative array a is assigned to b, and then the content of a is changed, why does b also change?

JS:
 var a = {"Client":"jQuery","Server":"PHP"};
 var b = a;
 a["New"] = "Element";
 console.log(b);
 // Output Object { Client="jQuery", Server="PHP", New="Element"}

 PHP routine 1:
 $a = array('Client'=>'jQuery','Server'=>'PHP');
 $b = $a;
 $a['New'] = 'Element';
 var_export($b);
 //Output array('Client'=>'jQuery','Server'=>'PHP')

 PHP routine 2:
 $a = array('Client'=>'jQuery','Server'=>'PHP');
 $b = &$a; //Reference assignment
 $a['New'] = 'Element';
 var_export($b);
 //Output array('Client'=>'jQuery','Server'=>'PHP','New'=>'Element')

In Javascript, when an associative array a is assigned to b, and then the content of a is changed, why does b also change?

Reply content:

JS:
 var a = {"Client":"jQuery","Server":"PHP"};
 var b = a;
 a["New"] = "Element";
 console.log(b);
 // Output Object { Client="jQuery", Server="PHP", New="Element"}

 PHP routine 1:
 $a = array('Client'=>'jQuery','Server'=>'PHP');
 $b = $a;
 $a['New'] = 'Element';
 var_export($b);
 //Output array('Client'=>'jQuery','Server'=>'PHP')

 PHP routine 2:
 $a = array('Client'=>'jQuery','Server'=>'PHP');
 $b = &$a; //Reference assignment
 $a['New'] = 'Element';
 var_export($b);
 //Output array('Client'=>'jQuery','Server'=>'PHP','New'=>'Element')

In Javascript, when an associative array a is assigned to b, and then the content of a is changed, why does b also change?

For non-ordinary types such as arrays (strings, integers, Boolean), your assignment is equivalent to address copying, that is, a and b occupy the same address. So if b is changed, a will also change. Essentially, a and b are the same thing.

This answer here is more detailed. Arrays are reference type values ​​and are stored in the heap. https://www.zhihu.com/questio…

I saw someone say on the Internet that when assigning values ​​in JS, original types (such as strings) are copied values, and reference types (such as associative arrays) are copied references.

var a = {"Client":"jQuery","Server":"PHP"};
 var b = JSON.stringify(a); //Convert to string and assign value
 a["New"] = "Element";
 console.log(JSON.parse(b)); //Convert back to associative array (object) when used
 //Output Object { Client="jQuery", Server="PHP"}

 IE8 does not support JSON.parse and JSON.stringify, so json2.js needs to be introduced:
 http://www.json.org/js.html
 https://github.com/douglascrockford/JSON-js/blob/master/json2.js
 Versions below IE9:
 

I feel that JS arrays are not as flexible as PHP. PHP supports & declaration reference assignment, and PHP arrays are “copy-on-write”:

echo round(memory_get_usage()/(1024*1024))."MB\n"; //0MB
 $a = file('/home/eechen/note.txt', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
 echo round(memory_get_usage()/(1024*1024))."MB\n"; //9MB
 $b = $a;
 echo round(memory_get_usage()/(1024*1024))."MB\n"; //9MB (the memory does not change after the assignment)
 $b['new'] = 'element';
 echo round(memory_get_usage()/(1024*1024))."MB\n"; //14MB (the memory changes after modification, that is, copy on write)

Because a and b both point to the same array.

If you want to keep it unchanged, first convert the object into a string, and then convert it back into an object. They will be two different objects. If used directly, it is actually one. The correct answer has been given above.