JavaScript function to check if a value is a valid decimal number

Other Questions JavaScript
1

Hey everyone! I’m trying to figure out the best way to check if a string is a valid decimal number in JavaScript. I want something simple and easy to understand that works across different browsers. Here’s what I’m looking for:

  1. It should return true for strings like ‘-1’, ‘-1.5’, ‘0’, ‘0.42’, and ‘.42’
  2. It should return false for things like ‘99,999’, ‘0x89f’, ‘#abcdef’, ‘1.2.3’, empty strings, and non-numeric text

I’ve tried a few different approaches but I’m not sure which one is the most reliable. Can anyone suggest a good solution? Maybe a function called isDecimal() or something similar? Thanks in advance for your help!

function isDecimal(value) {
  // Your code here
}

console.log(isDecimal('-1.5'));  // Should return true
console.log(isDecimal('abc'));   // Should return false

I’d really appreciate any tips or examples you can share!

2

I’ve dealt with this issue before, and I found that using a regular expression is the most straightforward approach. Here’s a function that’s worked well for me:

function isDecimal(value) {
  return /^-?\d*\.?\d+$/.test(value);
}

This regex checks for an optional minus sign, followed by zero or more digits, an optional decimal point, and then one or more digits. It’s pretty robust and handles all the cases you mentioned.

One thing to watch out for: this function will return true for integers too. If you strictly want to check for decimals with a fractional part, you could modify it slightly:

function isDecimal(value) {
  return /^-?\d*\.\d+$/.test(value);
}

This version requires a decimal point and at least one digit after it. Hope this helps!

3

hey Pete_Magic, here’s a quick n dirty solution that might work for ya:

function isDecimal(val) {
return !isNaN(parseFloat(val)) && val.includes(‘.’);
}

it’s not perfect but gets the job done for most cases. lmk if u need anything else!

4

While regular expressions can work, they’re not always the most reliable for number validation. I prefer using JavaScript’s built-in functions for this task. Here’s a simple approach that’s quite effective:

function isDecimal(value) {
const num = parseFloat(value);
return !isNaN(num) && isFinite(num) && String(num).indexOf(‘.’) !== -1;
}

This method converts the string to a number, checks if it’s valid and finite, and ensures it has a decimal point. It correctly handles all your examples and even works with scientific notation. Plus, it’s easy to understand and maintain. Just remember, it will return false for integers, which seems to be what you want based on your requirements.