{"componentChunkName":"component---src-templates-blog-post-js","path":"/keyword-this/","result":{"data":{"site":{"siteMetadata":{"title":"Noah's Web Dev Notes"}},"markdownRemark":{"id":"7ddbb1fd-8bfe-59c3-a3ae-6514e1d78309","excerpt":"‘this’ is a javascript keyword. It is an object automatically generated inside the function body when the function is running, and can only be used inside the…","html":"
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‘this’ is a javascript keyword. It is an object automatically generated inside the function body when the function is running, and can only be used inside the function body.

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this has different values depending on where it is used:

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this in a method
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In the example this refers to the person object. The person object is the owner of the fullName method.

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// Create an object:\nconst person = {\n  firstName: \"John\",\n  lastName: \"Doe\",\n  fullName : function() {\n    return this.firstName + \" \" + this.lastName; // this refers to person\n  }\n};\n\n// Display data from the object:\nconsole.log(person.fullName());
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this alone:
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let x = this;\nconsole.log(x) // Window
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this in a Function (default)
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In a JavaScript function, the owner of the function is the default binding for this. Because function could be considered as a method of the object Window. So, in a function, this refers to the Global object [object Window].

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function myFunction() {\n  return this; //Window\n}
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this in a Function (strict)
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JavaScript strict mode does not allow default binding. So, when used in a function, in strict mode, this is undefined.

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this in a constructor
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When using this inside a constructor, this refers to the object that been created by the constructor

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var x = 2;\nfunction Obj() {\n  this.x = 1;\n}\n\nvar obj = new Obj();\nconsole.log(obj.x) // 1\nconsole.log(x)  // 2
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this in Event Handlers
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In HTML event handlers, this refers to the HTML element that received the event

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For example, this refers to the button element below:

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<!DOCTYPE html>\n<html>\n    <body>\n        <button onclick=\"this.style.display='none'\">Click to Remove Me!</button> \n    </body>\n</html>
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Object Method Binding
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In these examples, this is the person object (The person object is the “owner” of the function):

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// Create an object:\nconst person = {\n  firstName  : \"John\",\n  lastName   : \"Doe\",\n  id     : 5566,\n  myFunction : function() {\n    return this;\n  }\n};\n\n// Display data from the object:\ndocument.getElementById(\"demo\").innerHTML = person.myFunction(); // [object Object]
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Explicit Function Binding
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The call() and apply() methods are predefined JavaScript methods. They can both be used to call an object method with another object as argument.

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In the example below, when calling person1.fullName with person2 as argument, this will refer to person2, even if it is a method of person1:

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const person1 = {\n  fullName: function() {\n    return this.firstName + \" \" + this.lastName;\n  }\n}\nconst person2 = {\n  firstName:\"John\",\n  lastName: \"Doe\",\n}\nlet x = person1.fullName.call(person2); \ndocument.getElementById(\"demo\").innerHTML = x; // John Doe
","frontmatter":{"title":"Javascript keyword:'this'","date":"December 14, 2020","description":"Let's discuss the meaning of 'this'."}},"previous":{"fields":{"slug":"/var-let-const/var-let-const/"},"frontmatter":{"title":"Difference between var, const and let?"}},"next":{"fields":{"slug":"/reference-value/"},"frontmatter":{"title":"Reference and value"}}},"pageContext":{"id":"7ddbb1fd-8bfe-59c3-a3ae-6514e1d78309","previousPostId":"d422e799-3251-5f86-900c-35e0e0b2f3ab","nextPostId":"c063f940-d1d1-5055-a113-1f6316505656"}},"staticQueryHashes":["2841359383","3257411868"]}