String API: string.trimStart()

string.trimStart() removes whitespace from the beginning of a string

• trimStart() method is defined on every string (on the prototype)

GIVEN a string starting with one space

• WHEN the string is only a space THEN trimStart leave an empty string
• WHEN followed by a word THEN just the word will be left
• WHEN followed by a word and then spaces THEN the word and the spaces after will be left
• WHEN trimming a right-to-left (RTL) string THEN spaces are still trimmed from the left side
• WHEN trimming a russian (cyrillic) string THEN gets trimmed on the left too
• WHEN followed by a UTF string THEN it also removes the leading space

GIVEN a string starting with any number of spaces

• WHEN starting without a space THEN trimStart() will leave the string as is
• WHEN starting with many spaces THEN those will be trimmed only at the start (left for a left-to-right language)
• WHEN trimming a RTL string THEN it spaces are removed from the left, ignoring the string direction
• WHEN a string starts with spaces and line breaks THEN those are removed too

additional knowledge

• WHEN trimStart() is called THEN the original string stays untouched
• trimLeft and trimStart are the same function

Links

mdn docs Description of `String.prototype.trimStart()` on MDN.
spec The specification describing `String.prototype.trimStart()`.
tests sourceCode The official tests for JavaScript (engines) for `trimStart`.