@@ -41,8 +41,12 @@ Top JavaScript interview questions
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| 33 | [ What are the different ways to empty an array in javascript] ( #33-what-are-the-different-ways-to-empty-an-array-in-javascript ) |
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| 34 | [ What is NaN in javascript] ( #34-what-is-nan-in-javascript ) |
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| 35 | [ Javascript naming convention] ( #35-javascript-naming-convention ) |
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- | 36 | [ Difference between call(), apply() and bind()] ( difference-between-call-apply-and-bind ) |
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-
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+ | 36 | [ Difference between call(), apply() and bind()] ( #36-difference-between-call-apply-and-bind ) |
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+ | 37 | [ What is the use of isNaN function] ( #37-what-is-the-use-of-isnan-function ) |
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+ | 38 | [ What is 'this' keyword in javascript] ( #38-what-is-this-keyword-in-javascript ) |
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+ | 39 | [ How do we add comments in javascript] ( #39-how-do-we-add-comments-in-javascript ) |
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+ | 40 | [ What is the use of typeof operator] ( #40-what-is-the-use-of-typeof-operator ) |
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+ | 41 | [ Is JavaScript case-sensitive] ( #41-is-javascript-case-sensitive ) |
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### 1. What is JavaScript
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* JavaScript is a scripting language used to create dynamic and interactive websites. It is supported by all major web browsers.
@@ -571,6 +575,56 @@ function printName(message) {
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let sayHello = printName .bind (person, " Hello" );
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sayHello ();
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` ` `
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+
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+ ### 37. What is the use of isNaN function
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+ isNaN() is a built-in JavaScript function. It takes a single argument and returns true if the argument is not a number, otherwise it returns false.
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+ ` ` ` js
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+ let num1 = 5 ;
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+ let num2 = " hi" ;
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+
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+ console .log (isNaN (num1)); // output ========> false
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+ console .log (isNaN (num2)); // output ========> true
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+ ` ` `
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+
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+ ### 38. What is 'this' keyword in javascript
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+ The value of 'this' is determined by the context in which it is used. In general, 'this' keyword refers to the object it belongs to.
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+ The 'this' keyword in JavaScript can have different values depending on where it is used -
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+ 1. If it is used inside a method, then it refers to the object that it belongs to
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+ 2. If it is used inside any function or alone (i.e outside any function or method), then it referes to the global object
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+ 3. If it is used in the context of an event handler, such as a click event, then it refers to the element that triggered the event
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+
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+ ### 39. How do we add comments in javascript
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+ **Single-line comments** - Add comments using 2 forward slashes //
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+ ` ` ` js
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+ // this is a single line comment
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+ ` ` `
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+ **Multi-line comments** - Enclose the text between /* and */
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+ ` ` ` js
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+ /*
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+ This is a
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+ multiline comment
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+ example
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+ */
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+ ` ` `
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+
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+ ### 40. What is the use of typeof operator
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+ The typeof operator returns a string that indicates the data type of the variable/value.
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+ ` ` ` js
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+ let var1 = " Surbhi" ;
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+ let var2 = 10 ;
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+ console .log (typeof var1); // output ========> "string"
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+ console .log (typeof var2); // output ========> "number"
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+ console .log (typeof " hello" ); // output ========> "string"
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+ console .log (typeof 2 ); // output ========> "number"
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+ console .log (typeof true ); // output ========> "boolean"
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+ ` ` `
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+
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+ ### 41. Is JavaScript case-sensitive
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+ Yes, JavaScript is a case-sensitive language. For e.g., the variables firstName and firstname are considered to be two different variables.
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+ ` ` ` js
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+ let firstName = " Surbhi" ;
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+ console .log (firstname); // output ========> Uncaught ReferenceError: firstname is not defined
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+ ` ` `
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******************************In progress
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