写一个方法去掉字符串中的空格

var str = '  a b c  d e  f g  ';

function removeSpace(value, type) {
    var headPattern = /^\s+/g;
    var tailPattern = /\s+$/g;
    var headAndTailPattern = /^\s+|\s+$/g;
    var middlePattern = /(\S)\s+(\S)/g;
    var pattern = /\s+/g;

    if (type === 'head') {
        return value.replace(headPattern, '');
    } else if (type === 'tail') {
        return value.replace(tailPattern, '');
    } else if (type === 'head_and_tail') {
        return value.replace(headAndTailPattern, '');
    } else if (type === 'middle') {
        while (middlePattern.exec(value)) {
            value = value.replace(middlePattern, '$1$2');
        }
        return value;
    } else {
        return value.replace(pattern, '');
    }
}