atom/src/text-utils.coffee at master · almoral/atom · GitHub

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isHighSurrogate = (string, index) ->

0xD800 <= string.charCodeAt(index) <= 0xDBFF

isLowSurrogate = (string, index) ->

0xDC00 <= string.charCodeAt(index) <= 0xDFFF

# Is the character at the given index the start of a high/low surrogate pair?

# string - The {String} to check for a surrogate pair.

# index - The {Number} index to look for a surrogate pair at.

# Return a {Boolean}.

isSurrogatePair = (string, index=0) ->

isHighSurrogate(string, index) and isLowSurrogate(string, index + 1)

# Get the number of characters in the string accounting for surrogate pairs.

# This method counts high/low surrogate pairs as a single character and will

# always returns a value less than or equal to `string.length`.

# string - The {String} to count the number of full characters in.

# Returns a {Number}.

getCharacterCount = (string) ->

count = string.length

count-- for index in [0...string.length] when isSurrogatePair(string, index)

count

# Does the given string contain at least one surrogate pair?

# string - The {String} to check for the presence of surrogate pairs.

# Returns a {Boolean}.

hasSurrogatePair = (string) ->

string.length isnt getCharacterCount(string)

module.exports = {getCharacterCount, isSurrogatePair, hasSurrogatePair}