# Disallow Number Literals That Lose Precision (no-loss-of-precision)

The `"extends": "eslint:recommended"`

property in a configuration file enables this rule.

This rule would disallow the use of number literals that immediately lose precision at runtime when converted to a JS `Number`

due to 64-bit floating-point rounding.

## Rule Details

In JS, `Number`

s are stored as double-precision floating-point numbers according to the IEEE 754 standard. Because of this, numbers can only retain accuracy up to a certain amount of digits. If the programmer enters additional digits, those digits will be lost in the conversion to the `Number`

type and will result in unexpected behavior.

Examples of **incorrect** code for this rule:

```
/*eslint no-loss-of-precision: "error"*/
const x = 9007199254740993
const x = 5123000000000000000000000000001
const x = 1230000000000000000000000.0
const x = .1230000000000000000000000
const x = 0X20000000000001
const x = 0X2_000000000_0001;
```

Examples of **correct** code for this rule:

```
/*eslint no-loss-of-precision: "error"*/
const x = 12345
const x = 123.456
const x = 123e34
const x = 12300000000000000000000000
const x = 0x1FFFFFFFFFFFFF
const x = 9007199254740991
const x = 9007_1992547409_91
```

## Version

This rule was introduced in ESLint 7.1.0.