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<!DOCTYPE html>
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        <title>call() || JS CodeyLuwak</title>
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        <header>
            <a href="./index.html"><h1>JavaScript: call()</h1></a>
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        <main class="js-notes">


            <article id="call-method">
                <h2>Function.prototype.call()</h2>

                <dl>
                    <dt><code>call()</code></dt>
                    <dd>
                        <code class="formula-thin">function <span class="variable">func</span>(<span class="variable">args</span>) {<span class="variable">...</span>}</code>
                    </dd>
                    <dd>
                        <code class="formula"><span class="variable">func</span>.call(<span class="variable">obj</span>, <span class="variable">args</span>)</code>
                    </dd>
                    <dd><code>call()</code> allows an <b>object's function</b> to be called for a <b>different object</b>. It provides a new value <code>this</code> to the function.</dd>

                    <dd>Or it can be a <b>generic object function</b> altogether, created independent of any existing object, but for object use. In this case, the <code>this</code> keyword inside the function will refert to the <code>global</code> if it's not in strict mode.</dd>

                    <dt>Syntax</dt>
                    <dd>
<pre class="formula">
call()
call(<span class="variable">obj</span>)
call(<span class="variable">obj</span>, <span class="variable">args</span>)
</pre>
                    </dd>

                    <dd>Parameters
                        <ul>
                            <li><code>obj</code>: The object the function is being called to. Refered as <code>this</code> from inside the function.</li>
                            <li><code>args</code>: comma separated arguments for the function</li>
                        </ul>
                    </dd>
                    <dd>Return value:
                        <ul>
                            <li>The result of calling the function with the specified <code>this</code> value and arguments.</li>
                        </ul>
                    </dd>

                    <dt><code>call()</code> vs <code>apply()</code></dt>
                    <dd><code>call()</code><br>
                        <code class="formula"><span class="variable">func</span>.call(<span class="variable">obj</span>, <span class="variable">arg1, arg2, ..., argN</span>)</code>
                    </dd>
                    <dd><code>apply()</code><br>
                        <code class="formula"><span class="variable">func</span>.apply(<span class="variable">obj</span>, [<span class="variable">arg1, arg2, ..., argN</span>])</code>
                    </dd>
                    <dd>Similarities:
                        <ul>
                            <li>Both are for calling a function to operate on an object.</li>
                        </ul>
                    </dd>
                    <dd>Differences:
                        <ul>
                            <li><code>apply()</code>: Function's arguments are given as an array.</li>
                            <li><code>call()</code>: Function's arguments are given as a comma separated list.</li>
                        </ul>
                    </dd>


                </dl>
                <a href="#top"><hr></a>

            </article>
            <article id="chaining-constructor">
                <h2>Using call() to chain constructors</h2>
                <dl>
                    <dt>Chaining constructors</dt>

                    <dd>Task: Chaining generic <code>Product</code> constructor with specialized constructors <code>Food</code> and <code>Toy</code>.</dd>

                    <dt>Generic <code>Product</code> object constructor</dt>

                    <dd>
                        <ul>
                            <li>Defined with 2 parameters: <code>name</code> and <code>price</code>.</li>
                        </ul>
                    </dd>
                    <dd>
<pre class="formula-thin">
function <span class="type">Product</span>(<span class="variable">name, price</span>) {
    <b>this</b>.<span class="variable">name</span>  = <span class="variable">name</span>;
    <b>this</b>.<span class="variable">price</span> = <span class="variable">price</span>;
}
</pre>
                    </dd>
                    <dt>Specialized <code>Food</code> and <code>Toy</code> object constructors</dt>
                    <dd>
                        <ul>
                            <li>Invoke Product using <code>call()</code>, passing <code>this</code>, <code>name</code>, and <code>price</code>.</li>
                            <li><code>Product</code> initializes the properties <code>name</code> and <code>price</code>, then the specialized constructor define the <code>category</code>.</li>
                        </ul>
                    </dd>
                    <dd>
<pre class="formula-thin">
function <span class="type">Food</span>(<span class="variable">name, price</span>) {
  <span class="formula-thin"><span class="type">Product</span>.call(<span class="type">this</span>, <span class="variable">name, price</span>);</span>
    <b>this</b>.<span class="variable">categeory</span> = <span class="variable">"food"</span>;
}

function <span class="type">Toy</span>(<span class="variable">name, price</span>) {
    <span class="type">Product</span>.call(<span class="type">this</span>, <span class="variable">name, price</span>);
    <b>this</b>.<span class="variable">categeory</span> = <span class="variable">"toy"</span>;
}
</pre>
                    </dd>

                    <dt>Create objects with <code>new</code> keyword</dt>
                    <dd>
<pre class="formula-thin">
const <span class="variable">cheese</span> = new <span class="type">Food</span>(<span class="variable">"feta", 5</span>);
const <span class="variable">bread</span> = new <span class="type">Food</span>(<span class="variable">"muffin", 3</span>);
const <span class="variable">fun</span> = new <span class="type">Toy</span>(<span class="variable">"robot", 12</span>);
const <span class="variable">ocean</span> = new <span class="type">Toy</span>(<span class="variable">"figurine", 2</span>);
</pre>
                    </dd>
                    <dt>Results</dt>
                    <dd>
<pre class="formula-thin">
<span class="variable">cheese</span>;     // <span class="type">Food</span> {<span class="variable">name: 'feta', price: 5, category: 'food'</span>}
<span class="variable">bread</span>;      // <span class="type">Food</span> {<span class="variable"><span class="variable"><span class="variable">name: "muffin", price: 3, category: 'food'</span></span></span>}
<span class="variable">fun</span>;        // <span class="type">Toy</span> {<span class="variable">name: 'robot', price: 12, category: 'toy'</span>}
<span class="variable">ocean</span>;      // <span class="type">Toy</span> {<span class="variable">name: 'figurine', price: 2, category: 'toy'</span>}
</pre>
                    </dd>

                </dl>
                <a href="#top"><hr></a>
            </article>

            <article id="anonymous-function-and-direct-call">
                <h2>Anonymous function and direct call()</h2>

                <dl>
                    <dt>Anonymous function and direct calling</dt>
                    <dd><code>call()</code> can be used to invoke anonymous function directly after stating it.</dd>
                    <dd>
<pre class="formula">
<span class="variable">(<b>function</b>() {...})</span>.<b>call</b>(<span class="variable">thisArg</span>)
</pre>
                    </dd>
                    <dt>For each items in an object array</dt>
                    <dd>
<pre class="formula">
for (<span class="variable">let i = 0; i < arr.length; i++</span>) {
    <span <span class="variable">(<b>function</b>() {...})</span>.<b>call</b>(<span class="variable">arr[i]</span>)
};
</pre>
                    </dd>
                    <dd>Don't forget keyword <code>this</code></dd>

                    <dt>Task</dt>
                    <dd>Create anonymous function for printing content of each properties in an object array, with index numbering but starting from 1.</dd>

                    <dt>Basic way</dt>
                    <dd>
<pre class="formula-thin">
const <span class="variable">animals</span> = [
    {<span class="variable">species: "Dodo", name: "Dottie"</span>},
    {<span class="variable">species: "Flummel", name: "Op"</span>},
    {<span class="variable">species: "Flummel", name: "Ed"</span>}
];

for (<span class="variable">let i = 0; i < animals.length; i++</span>) {
    <span class="variable">console.log(`#${i+1} ${animals[i].species}: ${animals[i].name}`);</span>
};

<span class="comment">----------------
#1 Dodo: Dottie
#2 Flummel: Op
#3 Flummel: Ed
----------------</span>
</pre>
                    </dd>

                    <dt>Using function</dt>
                    <dd>
<pre class="formula-thin">
const <span class="variable">animals</span> = [
    {<span class="variable">species: "Dodo", name: "Dottie"</span>},
    {<span class="variable">species: "Flummel", name: "Op"</span>},
    {<span class="variable">species: "Flummel", name: "Ed"</span>}
];

function print(arr, i) {
    <span class="variable">console.log(`#${i+1} ${arr[i].species}: ${arr[i].name}`);</span>
}

for (<span class="variable">let i = 0; i < animals.length; i++</span>) {
    print(animals, i)
};

<span class="comment">----------------
#1 Dodo: Dottie
#2 Flummel: Op
#3 Flummel: Ed
----------------</span>
</pre>
                    </dd>

                    <dt>Using anonymous function and direct <code>call()</code></dt>
                    <dd>Working from the <code>print</code> function above</dd>
                    <dd>
                        <ul>
                            <li>The <code>this</code> is <code>animals[i]</code></li>
                            <li>Then the call: <code>call(animals[i], i)</code></li>
                            <li>And inside the function: <code>this.species</code> and <code>this.name</code></li>
                            <li>Parameters <code>arr</code> and <code>i</code> are not necessary</li>
                        </ul>
                    </dd>
                    <dd>From this:</dd>
                    <dd>
<pre class="formula-thin">
const <span class="variable">animals</span> = [
    {<span class="variable">species: "Dodo", name: "Dottie"</span>},
    {<span class="variable">species: "Flummel", name: "Op"</span>},
    {<span class="variable">species: "Flummel", name: "Ed"</span>}
];

for (<span class="variable">let i = 0; i < animals.length; i++</span>) {
    (function (arr, i) {
        <span class="variable">console.log(`#${i+1} ${arr[i].species}: ${arr[i].name}`);</span>
    }).call(animals[i], animals, i)
};

<span class="comment">----------------
#1 Dodo: Dottie
#2 Flummel: Op
#3 Flummel: Ed
----------------</span>
</pre>
                    </dd>
                    <dd>To this:</dd>
                    <dd>
<pre class="formula-thin">
const <span class="variable">animals</span> = [
    {<span class="variable">species: "Dodo", name: "Dottie"</span>},
    {<span class="variable">species: "Flummel", name: "Op"</span>},
    {<span class="variable">species: "Flummel", name: "Ed"</span>}
];

for (<span class="variable">let i = 0; i < animals.length; i++</span>) {
    (function () {
        <span class="variable">console.log(`#${i+1} ${this.species}: ${this.name}`);</span>
    }).call(animals[i])
};

<span class="comment">----------------
#1 Dodo: Dottie
#2 Flummel: Op
#3 Flummel: Ed
----------------</span>
</pre>
                    </dd>
                </dl>
                <a href="#top"><hr></a>
            </article>

            <article id="invoke-function-containing-this">
                <h2>Invoke object functions and give context to "this"</h2>

                <dl>
                    <dt>Invoke object functions and give context to "this"</dt>
                    <dd>Functions can be made for use in object. Inside function, the object is refered as <code>this</code>. Function then could be invoke conveniently using <code>call(object)</code>.</dd>
                    <dd>
<pre class="formula">
function <span class="variable">func</span> () { <span class="variable">this.property...</span> }

const <span class="variable">obj</span> = { <span class="variable">property1: "value1", property2: "value2", ...</span> }

<span class="variable">func</span>.call(<span class="variable">obj</span>)
</pre>
                    </dd>
                    <dt>Example</dt>
                    <dd>
<pre class="formula-thin">
function <span class="variable">dimension</span> () {
    <span class="variable">console.log(`The ${this.type} paper size is ${this.width} inch by ${this.length} inch.`)</span>;
};

const <span class="variable">letter</span> = {
    <span class="variable">type:   "letter",
    width:  8.5,
    length: 11</span>
};

<span class="variable">dimension</span>.call(<span class="variable">letter</span>);

<span class="comment">// The letter paper size is 8.5 inch by 11 inch.</span>
</pre>
                    </dd>
                </dl>
                <a href="#top"><hr></a>
            </article>

            <article id="blank-call-invokes-global-object">
                <h2>Blank call() to invoke global value</h2>

                <dl>
                    <dt>Blank <code>call()</code> to invoke global value</dt>
                    <dd>When <code>thisArg</code> is not given, global value is used. Because without context, <code>this</code> referes to the global object.</dd>
                    <dd>We can set a global values as default <code>this.property</code> values. This will be used when the <code>thisArg</code> is not given as an argument when calling.</dd>
<pre class="formula">
function <span class="variable">func</span> () { <span class="variable">this.property...</span> }

const <span class="variable">obj</span> = { <span class="variable">property1: "value1", property2: "value2", ...</span> }

<span class="variable">func</span>.call(<span class="variable">obj</span>)
</pre>
                    </dd>
                    <dt>Task</dt>
                    <dd>Create <code>welcome</code> function that can send welcome message to name within an object, to all objects in an array (through a for function), and give default <code>Guest</code> for use when there's no specific object.</dd>
                    <dd>
<pre class="formula-thin">
var <span class="variable">name</span> = <span class="variable">"Guest"</span>;

function <span class="variable">welcome</span>() {
    <span class="variable">console.log(`Welcome, ${this.name}!`);</span>
};

const <span class="variable">son</span> = { <span class="variable">name: "Dodo", age: 5</span> };

const <span class="variable">children</span> = [
    { <span class="variable">name: "Dottie", age: 5</span> },
    { <span class="variable">name: "Ed", age: 3</span> },
    { <span class="variable">name: "Op", age: 2</span> }
];
</pre>
                    </dd>
                    <dt>One function for all</dt>
                    <dd>Just the one function can suit default, single object, and array of objects:</dd>
                    <dd>
<pre class="formula-thin">
<span class="variable">welcome</span>.<b>call</b>();
<span class="comment">// Welcome, Guest!</span>

<span class="variable">welcome</span>.<b>call</b>(<span class="variable">son</span>);
<span class="comment">// Welcome, Dodo!</span>

<span class="variable">children</span>.<b>forEach</b>(<span class="variable">el</span> <b>=&gt;</b> <span class="variable">welcome</span>.<b>call</b>(<span class="variable">el</span>));<span class="comment">
// Welcome, Dottie!
// Welcome, Ed!
// Welcome, Op!</span>
</pre>
                    </dd>
                    <dd>Other outcomes:</dd>
                    <dd>
<pre class="formula-thin">
<span class="variable">welcome</span>();
<span class="variable">welcome</span>(<span class="variable">son</span>);
<span class="variable">welcome</span>(<span class="variable">children</span>);
<span class="comment">// Welcome, Guest!</span>

<span class="variable">welcome</span>.<b>call</b>(<span class="variable">children</span>);
<span class="comment">// Welcome, undefined!</span>
</pre>
                    </dd>
                    <dt>Doesn't work on strict mode <code>"use strict"</code></dt>
                    <dd>
<pre class="formula-thin">
<b>"use strict"</b>
var <span class="variable">name</span> = <span class="variable">"Guest"</span>;

function <span class="variable">welcome</span>() {
    <span class="variable">console.log(`Welcome, ${this.name}!`);</span>
};

<span class="variable">welcome</span>();
<span class="variable">welcome</span>.call();
<span class="comment">// Uncaught TypeError...</span>
</pre>
                </dl>
                <a href="#top"><hr></a>
            </article>

            <article id="references">
                <h2>References</h2>
                <ul>
                    <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call" target="_blank">MDN: Function.prototype.call()</a></li>
                </ul>
            </article>
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