trim.md

Javascript trim

With many keyboard layouts, a whitespace character may be entered through the use of a spacebar. Horizontal whitespace may also be entered on many keyboards through the use of the Tab ↹ key, although the length of the space may vary. Vertical whitespace is a bit more varied as to how it is encoded, but the most obvious in typing is the ↵ Enter result which creates a 'newline' code sequence in applications programs. Older keyboards might instead say Return, abbreviating the typewriter keyboard meaning 'Carriage-Return' which generated an electromechanical return to the left stop (CR code in ASCII-hex &0D;) and a line feed or move to the next line (LF code in ASCII-hex &0A;); in some applications these were independently used to draw text cell based displays on monitors or for printing on tractor-guided printers—which might also contain reverse motions/positioning code sequences allowing text-based output devices to achieve more sophisticated output. Many early computer games used such codes to draw a screen (e.g. Kingdom of Kroz), and word processing software would use this to produce printed effects such as bold, underline, and strikeout.

The term "whitespace" is based on the resulting appearance on ordinary paper. However they are coded inside an application, whitespace can be processed the same as any other character code and programs can do the proper action as defined for the context in which they occur.

whitespace characters in the Unicode Character Database

代码示例:

String.prototype.trim = function () {
  let str = this;
  // 潜在的空格编码
  const whitespace = " \n\r\t\f\x0b\xa0\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200a\u200b\u2028\u2029\u3000";

  // 不断循环取 string 第一个字符，直到第一个字符不是空格，则直接截取保留剩下的字符串。
  for (var i = 0, len = str.length; i < len; i++) {
    if (whitespace.indexOf(str.charAt(i)) === -1) {
      str = str.substring(i);
      break;
    }
  }

  // 跟上一步类似，不断循环取 string 最后一个字符，直到最后一个字符不是空格
  // 为什么要两个 for 循环？因为如果字符串的长度是 10,000 个字符，前后分开取，不用遍历中间非空格的字符串，可以节省大量的时间。
  for (i = str.length - 1; i >= 0; i--) {
    if (whitespace.indexOf(str.charAt(i)) === -1) {
      str = str.substring(0, i + 1);
      break;
    }
  }
  // 判断两次循环以后的字符串，是否是空字符串。
  return whitespace.indexOf(str.charAt(0)) === -1 ? str : '';
}

const newString = "        sadf       ".trim();
console.log(newString);