SpiderMonkey

SpiderMonkey is Mozilla's Javascript engine written in C/C++. It is used in various Mozilla products, including Firefox, and is available under the MPL2.

Example code

   1 #!/usr/bin/js
   2 function CTest(){
   3   this.counter=0;
   4 }
   5 
   6 
   7 CTest.prototype.increment=function(){
   8   this.counter++;
   9 };
  10 
  11 CTest.prototype.show=function(){
  12   putstr(this.counter);
  13   putstr("\r\n");
  14 };
  15 
  16 var c = new CTest();
  17 var d = new CTest();
  18 c.increment();
  19 c.increment();
  20 c.increment();
  21 c.show();
  22 
  23 d.increment();
  24 d.increment();
  25 d.show();

Run it with:

• chmod 755 test.js
• ./test.js

SpiderMonkey is installed on Slackware 14.

Windows binary

• https://archive.mozilla.org/pub/firefox/nightly/latest-mozilla-central/jsshell-win64.zip

Example of prototype/inheritance

• https://developer.mozilla.org/en/docs/Web/JavaScript/Inheritance_and_the_prototype_chain

When it comes to inheritance, JavaScript only has one construct: objects. Each object has an internal link to another object called its prototype (proto).

JavaScript objects are dynamic "bags" of properties (referred to as own properties). JavaScript objects have a link to a prototype object.

// https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects
var a = {"key":"A value"};
var b = {};
b.__proto__ = a; // set a as prototype of b . b inherits a 
/*var b = Object.create( a );*/
b.other="aaaa";
if( ! b.hasOwnProperty('key') ) print( "b doesn't have own property key" );
if( b.hasOwnProperty('other') ) print( b.other );

if( a.hasOwnProperty('key') ) print( a['key'] );
if( a.hasOwnProperty('other') ) print( a['other'] );

b.key='Other Value'; // b has own key "key" and a has also key "key" with different value

print('\nkeys in object a');
for(var key in a){
    print( key ,'->' , a[key] );
}

print('\nKeys in object b');
for(var key in b){
  print( key ,'->' , b[key] );
}

print('Value for key in prototype of b' , b.__proto__.key );

//-------
print();
function f(){
  this.propx='asdf';
  this.fn=function(){print("aaaa");};
  this.nr=123.4;
}

f.prototype.protoFn=function(){ print("bbb"); };

var x = new f();
print('x instance of f '  , x instanceof f);
print('x is type of ' + typeof f);
print('x instance of object '  , x instanceof Object);
print('x instance of Array '  , x instanceof Array);

for(var key in x){
  print( key ,':' , x[key] , x.hasOwnProperty(key) , typeof x[key]  );
}

print( JSON.stringify( x ) );