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Introduction to JavaScript

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  1. JavaScript: Basics
    9Topics
    |
    10 Quizzes
  2. JavaScript: Variables
    9Topics
    |
    10 Quizzes
  3. JavaScript: Conditional Statements
    10Topics
    |
    11 Quizzes
  4. JavaScript: Functions
    10Topics
    |
    11 Quizzes
  5. JavaScript: Scope
    6Topics
    |
    7 Quizzes
  6. JavaScript: Arrays
    11Topics
    |
    12 Quizzes
  7. JavaScript: Loops
    8Topics
    |
    9 Quizzes
  8. JavaScript: High Order Functions
    3Topics
    |
    3 Quizzes
Lesson 4, Topic 6
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JavaScript: Return

Yasin Cakal 7 Nov 2021
Lesson Progress
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When a function is called, the computer runs through the code of the function and evaluates the result of calling it. The resultant value is undefined by default.

function squarePerimeter(legnth){
  perimeter= legnth*4;
}

console.log(squarePerimeter(10));

//Output: undefined

In the example above, We defined our function to calculate the perimeter of a square by taking length as a parameter. The squarePerimeter() is then called with argument 10. However, when we tried to print the results, they were undefined. Is it possible that we wrote our function incorrectly? No! In fact, the function worked as expected, and the computer calculated the perimeter to be 40 feet, but we failed to record it. So, what is the best way to go about it? Using the keyword return!

function squarePerimeter(legnth){
  perimeter= legnth*4;
  return perimeter;
}

console.log(squarePerimeter(10));

//Output: 40

A return statement is used to return information from a function call. We use the return keyword followed by the value we want to return to create a return statement. If the value is omitted, undefined is returned instead, as we saw earlier.

When a return statement is used in the body of a function, the function’s execution is stopped, and the code after it is not executed. Take a look at the following example:

function squarePerimeter(length) {
  if (length < 0) {
    return 'You need positive integer to calculate perimeter!';
  }
  return 4*length;
}

console.log(squarePerimeter(-9));

//Output: You need positive integer to calculate perimeter!

If the length argument is less than 0, squarePerimeter() will return You need positive integer to calculate perimeter! The second return statement, 4*length, will not be executed.

Because it allows functions to produce output, the return keyword is extremely useful. The output can then be saved to a variable for later use.

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