String replaceFirst(
Pattern from,
String to,
[int startIndex = 0]
)

Returns a new string in which the first occurence of from in this string is replaced with to, starting from startIndex:

'0.0001'.replaceFirst(new RegExp(r'0'), ''); // '.0001'
'0.0001'.replaceFirst(new RegExp(r'0'), '7', 1); // '0.7001'

Source

/**
 * Returns a new string in which the first occurence of [from] in this string
 * is replaced with [to], starting from [startIndex]:
 *
 *     '0.0001'.replaceFirst(new RegExp(r'0'), ''); // '.0001'
 *     '0.0001'.replaceFirst(new RegExp(r'0'), '7', 1); // '0.7001'
 */
String replaceFirst(Pattern from, String to, [int startIndex = 0]);