radix

Enforce the consistent use of the radix argument when using parseInt()

When using the parseInt() function it is common to omit the second argument, the radix, and let the function try to determine from the first argument what type of number it is. By default, parseInt() will autodetect decimal and hexadecimal (via 0x prefix). Prior to ECMAScript 5, parseInt() also autodetected octal literals, which caused problems because many developers assumed a leading 0 would be ignored.

This confusion led to the suggestion that you always use the radix parameter to parseInt() to eliminate unintended consequences. So instead of doing this:

const num = parseInt("071");      // 57
1

Do this:

const num = parseInt("071", 10);  // 71
1

ECMAScript 5 changed the behavior of parseInt() so that it no longer autodetects octal literals and instead treats them as decimal literals. However, the differences between hexadecimal and decimal interpretation of the first parameter causes many developers to continue using the radix parameter to ensure the string is interpreted in the intended way.

On the other hand, if the code is targeting only ES5-compliant environments passing the radix 10 may be redundant. In such a case you might want to disallow using such a radix.

Rule Details

This rule is aimed at preventing the unintended conversion of a string to a number of a different base than intended or at preventing the redundant 10 radix if targeting modern environments only.

Options

There are two options for this rule:

• "always" enforces providing a radix (default)
• "as-needed" disallows providing the 10 radix

always

Examples of incorrect code for the default "always" option:

/*eslint radix: "error"*/

const num = parseInt("071");

const num1 = parseInt(someValue);

const num2 = parseInt("071", "abc");

const num3 = parseInt("071", 37);

const num4 = parseInt();
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10
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Examples of correct code for the default "always" option:

/*eslint radix: "error"*/

const num = parseInt("071", 10);

const num1 = parseInt("071", 8);

const num2 = parseFloat(someValue);
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2
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as-needed

Examples of incorrect code for the "as-needed" option:

/*eslint radix: ["error", "as-needed"]*/

const num = parseInt("071", 10);

const num1 = parseInt("071", "abc");

const num2 = parseInt();
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Examples of correct code for the "as-needed" option:

/*eslint radix: ["error", "as-needed"]*/

const num = parseInt("071");

const num1 = parseInt("071", 8);

const num2 = parseFloat(someValue);
1
2
3
4
5
6
7

When Not To Use It

If you don’t want to enforce either presence or omission of the 10 radix value you can turn this rule off.

Version

This rule was introduced in ESLint v0.0.7.

Further Reading

parseInt Radix
davidwalsh.name

Resources

• Rule source
• Tests source