Difference between these codes in the if block

Question

I get the expected result here.

 var modeObj = {};

array.forEach(num => {
    if (!modeObj[num])
        modeObj[num] = 0;
        modeObj[num]++;
});

I get an empty result here.

var modeObj = {};

array.forEach(num => {
    if (!modeObj[num]) {
        modeObj[num] = 0;
    }else {
        modeObj[num]++;
    }

});

How is the above code different from the one below? I'm missing some concept in the if condition.

If you indent your code correctly you might see what's wrong. — Barmar, Apr 08 '20 at 23:35
https://stackoverflow.com/questions/359732/why-is-it-considered-a-bad-practice-to-omit-curly-braces?lq=1 — Barmar, Apr 08 '20 at 23:36

score 3 · Accepted Answer · answered Apr 08 '20 at 23:36

When you have if/else - the line inside the else block will only gets evaluated when the value of the if is false.

In your first example - the second line will run every time, whether the if is valid or not.

If you don't have brackets - only the next line (after the if) is evaluated.
Your first example is actually the following:

var modeObj = {};

array.forEach(num => {
    if (!modeObj[num]) {
        modeObj[num] = 0;
    }
    modeObj[num]++;
});

As you can see - the modeObj[num]++; will get evaluated every time (not only when the if is true).

score 3 · Answer 2 · answered Apr 08 '20 at 23:36

3

The first code if condition does not have {}. Hence only the first line is executed and the line modeObj[num]++; is executed no matter what the result of the if condition is.

In the second code, you have added an else.

answered Apr 08 '20 at 23:36

LearningEveryday

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score 2 · Answer 3 · answered Apr 08 '20 at 23:34

You're increasing modeObj[num]++ outside if part of the conditional & the second code snippet. It should be like so instead:

var modeObj = {};

array.forEach(num => {
    if (!modeObj[num]) {
        modeObj[num] = 0;
        modeObj[num]++;
    } else {
       // do something
    }

});

Difference between these codes in the if block

3 Answers3