 # JavaScript: Check whether a matrix is a diagonal matrix or not

## JavaScript Basic: Exercise-115 with Solution

Write a JavaScript program to check whether a matrix is a diagonal matrix or not. In linear algebra, a diagonal matrix is a matrix in which the entries outside the main diagonal are all zero (the diagonal from the upper left to the lower right).

Example:
[1, 0, 0], [0, 2, 0], [0, 0, 3] ]) = true
[1, 0, 0], [0, 2, 3], [0, 0, 3] ]) = false

Pictorial Presentation: Sample Solution:

HTML Code:

``````<!DOCTYPE html>
<html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title> Check whether a matrix is a diagonal matrix or not</title>
<body>

</body>
</html>
```
```

JavaScript Code:

``````function is_diagonal_matrix(user_matrix) {
for (var i = 0; i < user_matrix.length; i++) {
for (var j = 0; j < user_matrix.length; j++) {
if (i !== j && user_matrix[i][j] !== 0)
return false;
}
}
return true;
}

console.log(is_diagonal_matrix([[1, 0, 0], [0, 2, 0], [0, 0, 3] ]));
console.log(is_diagonal_matrix([[1, 0, 0], [0, 2, 3], [0, 0, 3] ]));
``````

Sample Output:

```true
false
```

Flowchart: ES6 Version:

``````function is_diagonal_matrix(user_matrix) {
for (let i = 0; i < user_matrix.length; i++) {
for (let j = 0; j < user_matrix.length; j++) {
if (i !== j && user_matrix[i][j] !== 0)
return false;
}
}
return true;
}

console.log(is_diagonal_matrix([[1, 0, 0], [0, 2, 0], [0, 0, 3] ]));
console.log(is_diagonal_matrix([[1, 0, 0], [0, 2, 3], [0, 0, 3] ]));
``````

Live Demo:

See the Pen javascript-basic-exercise-115 by w3resource (@w3resource) on CodePen.

What is the difficulty level of this exercise?

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## JavaScript: Tips of the Day

Parameter's value

```function getItems(fruitList, ...args, favoriteFruit) {
return [...fruitList, ...args, favoriteFruit]
}

getItems(["banana", "apple"], "pear", "orange")
```

...args is a rest parameter. The rest parameter's value is an array containing all remaining arguments, and can only be the last parameter! In this example, the rest parameter was the second parameter. This is not possible, and will throw a syntax error.

```function getItems(fruitList, favoriteFruit, ...args) {
return [...fruitList, ...args, favoriteFruit];
}

getItems(['banana', 'apple'], 'pear', 'orange');```
The above example works. This returns the array [ 'banana', 'apple', 'orange', 'pear' ].

Ref: https://bit.ly/3jFRBje