Javascript: Run a function defined outside this closure as if it were defined inside this closure -

i want have function accepts function b argument, , runs b defined within closure scope of a, i.e. has access local variables.

for example, simplistically:

var = function(b){   var localc = "hi";   b(); }  var b = function(){   console.log(localc); }  a(b); // log 'hi' 

the way have found use eval. ec6 give better options maybe?

you can make context explicit , pass b:

var = function(b){     var context = {         localc: "hi"     };     b(context); }  var b = function(context){     console.log(context.localc); }  a(b); // hi 

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you can use this new , prototype:

var = function() {     this.localc = "hi"; } a.prototype.b = function(context){     console.log(this.localc); }  var = new a(); a.b(); // hi 

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or without prototype:

var = function() {     this.localc = "hi"; }  var = new a(); a.b = function(context){     console.log(this.localc); }; a.b(); // hi 

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you can use this bind:

var = {     localc: "hi" }; function b(foo) {     console.log(this.localc, foo); } b.bind(a)("foo"); // hi foo // .call: b.call(a, "foo"); // hi foo 

bind sets context this. call takes context it's first argument.

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this 1 not good:

var = function(b){     var localc = "hi";     b.bind(this)(); // global object, need `new` create new scope }  var b = function(){     console.log(this.localc); } a(b); // undefined