Function call not displaying undefined value when an array is passed as param

Question

I have created the following function in JavaScript which is working as expected:

<script>
    function add(a, b, c) {
        document.write('A: ' + a + '<br>');
        document.write('B: ' + b + '<br>');
        document.write('C: ' + c + '<br>');
    }
add(10, 20);
</script>

Output:

A: 10
B: 20
C: undefined

However, the following function in JavaScript is not working as expected wherein it is not displaying undefined value

<script>
    function addArray(a = [101]) {
        document.write('A: ' + a[0] + '<br>');
        document.write('B: ' + a + '<br>');
        document.write('C: ' + c + '<br>');
    }
    addArray([110]);
</script>

Output:

A: 110
B: 110

As per my understanding the output should be as below:

Expected Output:

A: 110
B: 110
C: undefined

Also, what is difference between a[0] and a in the above example?

`c` is *undeclared*, you should be getting a ReferenceError in the console. — VLAZ, Apr 01 '20 at 22:31
To see the difference between `a[0]` and `a`, try `addArray([110, 111])` — Anurag Srivastava, Apr 01 '20 at 22:33
@VLAZ Since you already addressed that, I was answering the last line of the question — Anurag Srivastava, Apr 01 '20 at 22:35
Does this answer your question? [What is the scope of variables in JavaScript?](https://stackoverflow.com/questions/500431/what-is-the-scope-of-variables-in-javascript) — VLAZ, Apr 01 '20 at 22:36

DCR · Answer 1 · 2020-04-01T23:06:34.850

0

c is never declared

    function addArray(a=[101],c) {
        document.write('A: ' + a[0] + '<br>');
        document.write('B: ' + a + '<br>');
        document.write('C: ' + c + '<br>');
    }
    addArray([110,120]);

edited Apr 01 '20 at 23:06

answered Apr 01 '20 at 22:40

DCR

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score 0 · Answer 2 · answered Apr 01 '20 at 22:47

 The difference between a[0] and a is that a[0] is displaying the first index value of an 
 array and a is displaying all the values of the array.

 Imagine A=[100,200]
 document.write('A: ' + a[0] + '<br>');
 Would write 100
 document.write('A: ' + a + '<br>');
 Would write 100,200

Function call not displaying undefined value when an array is passed as param

Output:

Output:

Expected Output:

2 Answers2