stringSliceMethods

Reports usage of substring instead of slice for string operations.

✅ This rule is included in the ts logical presets.

JavaScript provides three methods for extracting substrings: slice(), substr(), and substring(). This rule encourages consistent use of slice() because:

substr() is deprecated and removed from the ECMAScript specification
substring() has confusing behavior: it auto-swaps arguments when start > end, and treats negative indices as 0
slice() has consistent, predictable behavior that matches Array.prototype.slice()

Examples

const 
const result: string
result = 
const text: string
text.
String.substr(from: number, length?: number): string
Gets a substring beginning at the specified location and having the specified length.
@deprecated ― A legacy feature for browser compatibility
@param ― from The starting position of the desired substring. The index of the first character in the string is zero.
@param ― length The number of characters to include in the returned substring.
substr(1, 5);

const 
const result: string
result = 
const text: string
text.
String.slice(start?: number, end?: number): string
Returns a section of a string.
@param ― start The index to the beginning of the specified portion of stringObj.
@param ― end The index to the end of the specified portion of stringObj. The substring includes the characters up to, but not including, the character indicated by end.
If this value is not specified, the substring continues to the end of stringObj.
slice(1, 6);

substring to slice

❌ Incorrect
✅ Correct

const 
const result: string
result = 
const text: string
text.
String.substring(start: number, end?: number): string
Returns the substring at the specified location within a String object.
@param ― start The zero-based index number indicating the beginning of the substring.
@param ― end Zero-based index number indicating the end of the substring. The substring includes the characters up to, but not including, the character indicated by end.
If end is omitted, the characters from start through the end of the original string are returned.
substring(1, 5);

const 
const result: string
result = 
const text: string
text.
String.slice(start?: number, end?: number): string
Returns a section of a string.
@param ― start The index to the beginning of the specified portion of stringObj.
@param ― end The index to the end of the specified portion of stringObj. The substring includes the characters up to, but not including, the character indicated by end.
If this value is not specified, the substring continues to the end of stringObj.
slice(1, 5);

Negative indices

❌ Incorrect
✅ Correct

const 
const last: string
last = 
const text: string
text.
String.substring(start: number, end?: number): string
Returns the substring at the specified location within a String object.
@param ― start The zero-based index number indicating the beginning of the substring.
@param ― end Zero-based index number indicating the end of the substring. The substring includes the characters up to, but not including, the character indicated by end.
If end is omitted, the characters from start through the end of the original string are returned.
substring(
const text: string
text.
String.length: number
Returns the length of a String object.
length - 3);

const 
const last: string
last = 
const text: string
text.
String.slice(start?: number, end?: number): string
Returns a section of a string.
@param ― start The index to the beginning of the specified portion of stringObj.
@param ― end The index to the end of the specified portion of stringObj. The substring includes the characters up to, but not including, the character indicated by end.
If this value is not specified, the substring continues to the end of stringObj.
slice(-3);

Options

This rule is not configurable.

When Not To Use It

If you’re maintaining legacy code that heavily uses substr() or substring() and refactoring would be too costly, you may need to disable this rule. Note that substr() is deprecated and may be removed from JavaScript engines in the future.

Equivalents in Other Linters

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