How to Check if a Number is Positive or Negative in JavaScript Using Math.sign()

Last updated: 27th June 2025

Let’s see an example using both the methods.

1) Using Comparison Operator

<script>
  const number = -5;

  const message = number < 0 
    ? `${number} is negative` 
    : `${number} is positive`;

    document.write(message);
</script>

In the example above, the < (less than) operator is used to determine whether the number is negative or positive.

While it's obvious that the assigned variable holds a negative value in this (above) example, such visual cues aren't available during complex calculations. In real-world scenarios, especially at runtime, implementing a condition like the one shown above becomes essential to accurately determine whether a number is negative or positive.

Now, guess what the above condition returns. Well, it returns a Boolean true or false. Do this to check…

<script>
  const number = -5;
  document.write (number < 0);
</script>

The output is true, since it’s a negative value.

2) Using Math.sign()

In JavaScript, you can use the ES6 Math.sign() function to determine whether a number is positive, negative, or zero. This method accepts a single numeric argument and returns 1, -1, 0, or -0 based on the value provided.

Here's the syntax:

Math.sign(number)

The function will return either of this …
1, -1, 0, -0, or NaN

The Math.sign() function returns the sign of a given number, rather than its actual value. It returns 1 for positive numbers, -1 for negative numbers, and 0 for a value of zero.

NaN denotes "Not a Number", in case the parameter (or the argument) is not a number.

Remember, the function is "case sensitive".

Now, let's see how the function works.

<script>
  const number = 17;

    let result;
    if (Math.sign(number) === 1) {
        result = "is positive";
    } else if (Math.sign(number) === -1) {
        result = "is negative";
    } else {
        result = "is zero";
    }

    document.write(`${number} ${result}`);
</script>

Difference between Comparison Operator and Math.sign() function

The key difference between using a "comparison operator" and the "Math.sign()" function in JavaScript lies in their return values. A comparison operator returns a Boolean value (true or false), whereas Math.sign() returns the sign of the number. 1 for positive, -1 for negative, and 0 for zero. Let's explore both methods side by side to see how they work in practice.

<script>
    const number = -7;

    // Method 1: Using Comparison Operator.
    let result1;
    if (number < 0) {
        result1 = "negative (comparison)";
    } else if (number > 0) {
        result1 = "positive (comparison)";
    } else {
        result1 = "zero (comparison)";
    }

    // Method 2: Using Math.sign().
    let result2;
    switch (Math.sign(number)) {
        case 1:
            result2 = "positive (Math.sign)";
            break;
        case -1:
            result2 = "negative (Math.sign)";
            break;
        case 0:
        case -0: // handles negative zero.
            result2 = "zero (Math.sign)";
            break;
    }

    document.write(`Using comparison: ${number} is ${result1}<br>`);
    document.write(`Using Math.sign(): ${number} is ${result2}`);
</script>

The above example demonstrates how both approaches deliver the same result but differ in syntax and return types, Boolean logic for "comparisons", numeric indicators for "Math.sign()".

Examples using Math.sign()

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