Providing a callback function along with the specific execution context for it to be executed

Question

Providing a callback function along with the specific execution context for it to be executed

myFn is a function that executes an asynchronous task and triggers the callback upon successful completion.

SearchController.prototype.show = function (query) {

    this.searchService.myFn(arg1, this.myCallback); //I want to preserve the reference of `this` here
};

SearchController.prototype.myCallback = function (err, result) {
    if(err) {
        this.onError(err);
        return;
    }

    this.onSuccess(result);
}

SearchController.prototype.onSuccess = function() {...)
SearchController.prototype.onError = function() {...)

It's evident that the context of this is lost within the callback. How can I retain the original value of this from the invocation of myFn?

javascript callback this

Answer 1

Answer №1

The responsibility of the `myFn` function should be to accept a context as a parameter and utilize it accordingly. Alternatively, you can modify the method signature and encase your call within an anonymous function that utilizes `Function.prototype.call`:

SearchController.prototype.show = function (query)
{
    var __this = this;
    this.searchService.myFn(function (){ __this.myCallback.call(__this, arg1); });
};

Here is a proposed structure for `myFn`:

SearchController.prototype.myFn = function (arg, callback, context)
{
    // Perform tasks.. upon completion:

    callback.call(context, arg);
};

If you have multiple arguments to apply, consider using `Function.prototype.apply`.

Answer 2

The responsibility of the `myFn` function should be to accept a context as a parameter and utilize it accordingly. Alternatively, you can modify the method signature and encase your call within an anonymous function that utilizes `Function.prototype.call`:

SearchController.prototype.show = function (query)
{
    var __this = this;
    this.searchService.myFn(function (){ __this.myCallback.call(__this, arg1); });
};

Here is a proposed structure for `myFn`:

SearchController.prototype.myFn = function (arg, callback, context)
{
    // Perform tasks.. upon completion:

    callback.call(context, arg);
};

If you have multiple arguments to apply, consider using `Function.prototype.apply`.

Providing a callback function along with the specific execution context for it to be executed

Answer №1

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