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Accessing 'this' inside the callback should reference my array


Accessing 'this' inside the callback should reference my array

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Accessing 'this' inside the callback should reference my array
Tag : javascript , By : user182203
Date : November 28 2020, 11:01 PM

this one helps. im kinda new at javascript so i have an function which is given an array and it filters its elements from the arguments it is passed. What i need though is to make 'this' inside the callback function to refference at my originalArray so that console.log(this); would acctually print [1,2,3]. Have in mind that i acctually need to this in these lines because i can only edit all those lines not add some more. , You can use call to execute a function in a given this context:
var callback = function() {
  console.log(this);
  console.log(arguments);
};

// Using call
callback.call([1,2,3], "A", "B", "C");

// Using apply
callback.apply([1,2,3], ["A", "B", "C"]);

// Using bind:
//  creates a new function bound to [1,2,3]
callback.bind([1,2,3])("A", "B", "C");
callback.bind([1,2,3], "A")("B", "C"); // etc.
function makeMultiFilter(array) {
    // What we track
    var originalArray = array;
    var currentArray = originalArray;
    return (function arrayFilterer(pred, callback) {
        // If filter not a function return current Array
        if (typeof pred !== "function")
            return currentArray;
        // Filter out things
        currentArray = currentArray.filter(pred);

        // If callback is a function, execute callback
        if (typeof callback === "function")
            callback.call(originalArray, currentArray);
            return arrayFilterer;
    });
}

var arrayFilterer = makeMultiFilter([1, 2, 3]);

// call arrayFilterer to filter out all the numbers not equal to 2
arrayFilterer(function(elem) {
    return elem != 2; // check if element is not equal to 2
}, function(currentArray) {
    console.log(this); // prints [1,2 3]
    console.log(currentArray); // prints [1,3]
}); // prints [1, 3]`

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Inside the callback in Array.prototype.map, reference the new array


Tag : javascript , By : Adrian Codrington
Date : March 29 2020, 07:55 AM
should help you out Array.prototype.map() returns a new array. I want to reference this new array inside the callback function passed as the argument to Array.prototype.map(). Can I do that? , You can't do it with .map(), but you can do it with .reduce():
someArray.reduce(function(rv, item, idx) {
  // rv is the return value, in this case your array
  rv.push({whatever: rv});
  return rv;
}, []);

JavaScript: Accessing variable inside callback


Tag : javascript , By : niel
Date : March 29 2020, 07:55 AM
With these it helps I'm trying to use the open-graph plugin in NodeJS to get a preview image for a vine. The OG result is correct, but I can't access result[i] from within the og callback - the variable is undefined. How can I access result[i] in the OG callback? , You need a closure, i keeps changing because og is async
Thing.find(function(err, result) {
    for (var i = 0; i < result.length; i++) {
        if ( result[i].attachment &&
             result[i].attachment.embed_type == 'vine') 
        {
            (function(res) {
                og(res.attachment.embed_url, function(err, meta) {
                    res.attachment.preview_image = meta.image;
                    res.save();
                });
            }(result[i]));
        }
    }
});

Accessing 'this' of an object inside promise callback (then)


Tag : javascript , By : UpperLuck
Date : March 29 2020, 07:55 AM
Does that help My real recommendation is not to use this or new at all (and you can use Object.create if you still want inheritance):
var SomeObject = function(config) {
    return {
        PromiseMethod1: function(){
            return somePromise(config.foo);
        },
        PromiseMethod2: function(x){
            return someOtherPromise(config.bar, x);
        }
    }
}

var instance = SomeObject({config: true});
instance.PromiseMethod1().then(instance.PromiseMethod2);
var SomeObject function(config) {
    this.config = config;
}

SomeObject.prototype.PromiseMethod1 = function(){
    return somePromise(this.config.foo);
}

SomeObject.prototype.PromiseMethod1 = function(x){
    return someOtherPromise(this.config.bar, x);
}

var instance = new SomeObject({config: true});
instance.PromiseMethod1().then(instance.PromiseMethod2.bind(instance)); //<- :(

Accessing instance variable inside of a callback function


Tag : javascript , By : August
Date : March 29 2020, 07:55 AM
may help you . Just bind your callback function to the correct context:
fs.readFile(file, (function (err, result) {
    console.log(this.craziness);
}).bind(this));

Accessing properties from inside callback ES2015


Tag : javascript , By : Yolanda N. Ceron
Date : March 29 2020, 07:55 AM
should help you out ES6 arrow functions do not override this
class ProfileManager {
  constructor($http) {
    this._http = $http;
    this.profile = {};
  }

  getUser(profile) {
     this._http(`/api/users/${user.id}`).then((response) => {
        this.profile = response.data; 
     });
 }
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