非标准
该特性是非标准的，请尽量不要在生产环境中使用它！
移除字符串左端的连续空白符.
string.trimLeft()trimLeft方法移除原字符串左端的连续空白符并返回,trimLeft方法并不会直接修改原字符串本身.
trimLeft下面的例子输出了小写的字符串"foo ":
var str = " foo "; alert(str.length); // 8 str = str.trimLeft(); alert(str.length); // 5 document.write( str );
StringString.fromCharCode()String.fromCodePoint() [Translate]String.prototype.anchor()String.prototype.big() [Translate]String.prototype.blink() [Translate]String.prototype.bold() [Translate]String.prototype.charAt()String.prototype.charCodeAt()String.prototype.codePointAt() [Translate]String.prototype.concat()String.prototype.endsWith()String.prototype.fixed() [Translate]String.prototype.fontcolor() [Translate]String.prototype.fontsize() [Translate]String.prototype.includes()String.prototype.indexOf()String.prototype.italics() [Translate]String.prototype.lastIndexOf()String.prototype.link()String.prototype.localeCompare() [Translate]String.prototype.match()String.prototype.normalize()String.prototype.quote()String.prototype.repeat()String.prototype.replace()String.prototype.search()String.prototype.slice()String.prototype.small() [Translate]String.prototype.split()String.prototype.startsWith()String.prototype.strike() [Translate]String.prototype.sub() [Translate]String.prototype.substr()String.prototype.substring()String.prototype.sup() [Translate]String.prototype.toLocaleLowerCase() [Translate]String.prototype.toLocaleUpperCase() [Translate]String.prototype.toLowerCase()String.prototype.toSource() [Translate]String.prototype.toString()String.prototype.toUpperCase()String.prototype.trim()String.prototype.trimLeft()String.prototype.trimRight()String.prototype.valueOf()String.prototype[@@iterator]() [Translate]String.raw()FunctionObjectObject.prototype.__defineGetter__()Object.prototype.__defineSetter__()Object.prototype.__lookupGetter__()Object.prototype.__lookupSetter__() [Translate]Object.prototype.hasOwnProperty()Object.prototype.isPrototypeOf()Object.prototype.propertyIsEnumerable()Object.prototype.toLocaleString()Object.prototype.toSource()Object.prototype.toString()Object.prototype.unwatch() [Translate]Object.prototype.valueOf()Object.prototype.watch()