trim函数

    <textarea id="text"></textarea>
    <button>clear</button>

    //去空白
    function clearFun(str) {
        str = str.replace(/^\s+/, ‘‘);
        for (var i = str.length - 1; i >= 0; i--) {
            if (/\S/.test(str.charAt(i))) {   
                str = str.substring(0, i + 1);
                break;
            }
        }
        return str;
    }


    document.getElementsByTagName(‘button‘)[0].onclick = function() {
        var text = document.getElementById(‘text‘).value; 
        var clearText = clearFun(text);
        document.getElementById(‘text‘).value = clearText;
    }