# JavaScript Check for an Empty, Null, or Undefined String

> Write a custom isEmpty function using the equality operator and trim to check whether a JavaScript value is null, undefined, or an empty whitespace string

**URL:** https://sentry.io/answers/how-do-i-check-for-an-empty-undefined-null-string-in-javascript/

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## The Problem

You want to check that a value is not an empty string, null, or undefined. How do you do this?

## The Solution

To check that a value is not an empty string, null, or undefined, you can create a custom function that returns `true` if a value is `null`, `undefined`, or an empty string and `false` for all other falsy values and truthy values:

```javascript
function isEmpty(value) {
  return (value == null || (typeof value === "string" && value.trim().length === 0));
}

console.log(isEmpty("cat")); // false
console.log(isEmpty(1)); // false
console.log(isEmpty([])); // false
console.log(isEmpty({})); // false
console.log(isEmpty(false)); // false
console.log(isEmpty(0)); // false
console.log(isEmpty(-0)); // false
console.log(isEmpty(NaN)); // false

console.log(isEmpty("")); // true
console.log(isEmpty("    ")); // true
console.log(isEmpty(null)); // true
console.log(isEmpty(undefined)); // true
```

The `isEmpty` function uses the [equality operator (`==`)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality) to check if the argument `value` is `null` or `undefined`. This works because if one of the operands is `null` or `undefined`, the other operand must be `null` or `undefined` for the equality comparison to return `true`. If the argument `value` is not `null` or `undefined`, the right side of the [logical OR (||) operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_OR) is evaluated.

To check for an empty string, the [logical && operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_AND) is used. The first operand uses the [`typeof`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof) operator to check if the argument `value` is a string. If the `value` is a string, leading and trailing white space and line terminator strings are removed using the [`trim()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trim) method. This logical && operator expression returns `true` if a string is empty or consists of white space and line terminator strings only.

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*Source: [sentry.io/answers/how-do-i-check-for-an-empty-undefined-null-string-in-javascript/](https://sentry.io/answers/how-do-i-check-for-an-empty-undefined-null-string-in-javascript/)*