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javascriptfunctionobjectprototypal-inheritancedelegation

JavaScript prototype delegation in function

I am trying to learn Javascript but I am finding this prototype concept very confusing someone helps me with this code snippet

var func = function (){};
func.prototype = {m:9};

func.prototype.m; // That logs 9

func.m; // That logs undefined

Why is the delegation not working in this case?

Solution

  • What you have is a constructor function that has m in its prototype.

    var func = function (){};
func.prototype = {m:9};

console.log( func.prototype.m ); // That logs 9

    The prototype is assigned not to the function itself but to instances created by this function:

    var f = new func();

console.log( f.m ); // That also logs 9

    This is where your m is.

    For this to also log 9 

    func.m

    you'd have to have m in Function.prototype because the prototype of func is Function

    Function.prototype.m = 9;

console.log( func.m ); // Logs 9