JavaScript prototype chain example sharing_javascript skills

Copy code The code is as follows: /* Each object instance has an attribute member that points to the prototype (prototype) of its instanceof object (tentatively called the parent object) We put this The relationship that points to the parent prototype layer by layer is called [prototype chain prototype chian] The prototype also has a parent prototype, because it is often also an object instance, unless we artificially change it In JavaScript, "Everything is is an object, and function is the first type. " Function and Object are both instances of functions. The parent prototype of Function points to the prototype of Function. The parent prototype of Function.prototype is the prototype of Object The parent prototype of Object also points to the prototype of Function. Object.prototype is the top level of all parent prototypes In In the spiderMonkey engine, the parent prototype can be accessed through __proto__ */ Function.prototype.hi = function(){alert('hi Function');} Object.prototype.hi = function( ){alert('hi Object');} var a = function(){ this.txt = "a"; } a.prototype = { say:function (){alert('a');} } alert(a instanceof Function);//a is an instance of Function; alert(a.__proto__ === Function.prototype);/ /a’s parent prototype points to Function’s prototype; alert(Function instanceof Object);//Function is an instance of Object; alert(Function.__proto__ === Function.prototype);//Function’s parent The prototype points to the prototype of Function; alert(Function.prototype.__proto__ === Object.prototype);//The parent prototype of Function’s prototype points to the prototype of Object alert(Object.__proto__ === Function .prototype);//The parent prototype of Object points to the prototype of Function; alert(Object.prototype.__proto__);//The prototype of Object is the top of all parent prototypes, and it no longer has a parent prototype;

alert(a.prototype instanceof Object);//The prototype of a is also an object alert(a.prototype.__proto__ === Object.prototype);//The parent prototype of a’s prototype points to the prototype of Object

var A = function(){}; A.prototype = new a(); A.prototype.say = function(){ alert('A'); } alert(A instanceof Function);//A is an instance of Function alert(A.__proto__ === Function.prototype);//The parent prototype of A points to the prototype of Function alert( A.prototype instanceof a);//The prototype of A is an instance of a alert(A.prototype.__proto__ === a.prototype);//The parent prototype of A’s prototype points to the prototype of a

var iA = new A();//iA is an instance of A, iA.__proto__ === A.prototype var iB = new a();//iB is an instance of a, iB.__proto__ === a.prototype iA.hi(); /* iA itself does not have a hi method (not in the structure, nor has it been defined itself), so find iA.__proto__ that is A.prototype was not found either. So I searched for A.prototype.__proto__, which is a.prototype, but still found nothing. I continued to search for a.prototype.__proto__, which is Object.prototype. Wow, I found it hi , so call it and stop looking for Output: hi Object */ iB.hi(); /* iB itself has no hi method (not in the constructor, nor defined by itself) (passed), So I looked for iB.__proto__, which is a.prototype, and still didn’t find it. I continued to look for a.prototype.__proto__, which is Object.prototype. Wow, I found hi, so I called it and stopped searching Output: hi Object */ a.hi(); /* a itself has no hi method (not in the construction, and has not been defined by itself), so find a.__proto__ is both Function.prototype, wow, I found hi, so I called it and stopped looking for Output: hi Function */ iA.say(); /* iA itself has no say method (not in the structure, and has not been defined by itself), so I looked for iA.__proto__, which is A.prototype, wow, I found say, so I called it and stopped searching So, call it here The output of A.prototype.say is: A */ iB.say(); /* iB itself has no say method (not in the construction, nor has it been defined by itself) ), So I looked for iB.__proto__, which is a.prototype, wow, I found say, so I called it and stopped searching So, what was called here was a.prototype.say Output: a */ iA.bad(); /* iA itself has no bad method (not in the structure, and has not been defined by itself), so I looked for iA.__proto__, which is A.prototype , also not found, So I searched for A.prototype.__proto__, that is, a.prototype, but still found nothing. I continued to search for a.prototype.__proto__, that is, Object.prototype, and finally couldn't find it, so I stopped searching. Return error, iA.bad is not a function */ // -->

Thanks to simon for the correction! All instances will not search for their own prototype when searching for attribute methods (the prototype of the instance is not in the prototype chain and can only be used as an attribute)!

JavaScript prototype chain example sharing_javascript skills

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