一行就足够了：

var x = '|f|oo||';

var y = x.replace(/^\|+|\|+$/g, '');

document.write(x + '<br />' + y);


^\|+   beginning of the string, pipe, one or more times
|      or
\|+$   pipe, one or more times, end of the string

在功能上：

function trim (s, c) {

  if (c === "]") c = "\\]";

  if (c === "\\") c = "\\\\";

  return s.replace(new RegExp(

    "^[" + c + "]+|[" + c + "]+$", "g"

  ), "");

}



chars = ".|]\\";

for (c of chars) {

  s = c + "foo" + c + c + "oo" + c + c + c;

  console.log(s, "->", trim(s, c));

}