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# Number Truncation in JavaScript Use `Math.trunc()` to truncate a floating point number and return its integer part. This function doesn't do any rounding, it simply removes all the digits following the decimal. Now you have a whole number, yay 🎊

``````const number = 80.6

// Old Way
number < 0 ? Math.ceil(number) : Math.floor(number);
// 80

// ✅ES6 Way
const es6 = Math.trunc(number);
// 80
``````

### Example

`Math.trunc()` simply truncates (cuts off) the dots and the digits to the right of it. No matter whether the argument is a positive or negative number.

``````Math.trunc(80.9); // 80
Math.trunc(80.8); // 80
Math.trunc(80.8); // 80
Math.trunc(80.6); // 80
Math.trunc(80.5); // 80
Math.trunc(80.4); // 80
Math.trunc(80.3); // 80
Math.trunc(80.2); // 80
Math.trunc(80.1); // 80

Math.trunc(-80.1); // -80
``````

Now let's see some examples with non-number arguments:

``````Math.trunc('80.1'); // 80
Math.trunc('hello'); // NaN
Math.trunc(NaN); // NaN
Math.trunc(undefined); // NaN
Math.trunc(); // NaN
``````

## Number truncation using `parseInt`

You can get a similar result using `parseInt`

``````parseInt(80.1); // 80
parseInt(-80.1); // -80

parseInt('80.1'); // 80
parseInt('hello'); // NaN
parseInt(undefined); // NaN
parseInt(); // NaN
``````

### `Math.trunc()` vs `parseInt()`

`parseInt` is mainly used for a string argument. So if you're dealing with numbers, it's way better to use `Math.trunc()`.

If you're curious, I wrote up a performance test comparing these two functions.

jsPerf: Math.trunc vs parseInt

### The gotcha with `parseInt`

There's a potential issue when using `parseInt`. When you pass in an argument that's not a string, in our case a number, it will first convert the value to a string using the `toString()` abstract operation. Most of the time, `parseInt` is fine. But let's look at an example where it might not be.

``````const number = 1000000000000000000000.5;

const result = parseInt(number);

console.log(result); // 1 <-- 😱
``````

☝️So why did this happen?? That's because our argument is not a `string`, so the first thing `parseInt` does is it will convert the argument into a `string`.

``````const number = 1000000000000000000000.5;

const result = number.toString();

console.log(result); // "1e+21"
``````

So when it tried to grab the integer from `1e+21`, it just knows to grab the `1` value. So, using `parseInt` definitely has its gotcha. Because of this edge case, you might want to consider using the `Math` functions 👍

## Browser Support

Most modern browsers support `Math.trunc()`. EXCEPT, Internet Explorer. I know 😞 So if you need support for older browsers, use the old way 😕

Browser Support: Math.trunc

## Community Input

### Bitwise Operator Solutions

Double Bitwise NOT `~~`

``````console.log(~~80.6); // 80
``````

Thanks: @Jorgert120

Bitwise OR `|`

``````console.log(80.6 | 0); // 80
``````

Thanks: @mac_experts

## Resources

Thanks for reading ❤
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## Discussion (6)  Ben Sinclair

I didn't know about `trunc` and I would have just used `parseInt` without giving it a thought, but that gotcha you explain is a good point.

Unless I was mimimising/golfing or there's a tiny performance benefit and you're performing the operation a gazillion times per second, I'd stay clear of the bitwise tricks. They're curiosities but they make the code difficult to read. Samantha Ming

I guess bitwise operators are not as popular, so if you use it in your code it’s probably going to make a few people spin their heads as to what’s going on 😵... honestly, I have never used bitwise operator in my code before 😥 do you know if there are any other gotcha with using bitwise operators?