Edit in JSFiddle

$('#test').click(function()
{

    var message = '';
    
    var result_1A = 'some_text_for_test'.startsWith('some');  //應回傳true
    var result_1B = 'some_text_for_test'.startsWith('error'); //應回傳false
    
    message += 'startsWith result_1A : ' + result_1A + '</br>';
    message += 'startsWith result_1B : ' + result_1B + '</br>';
    
    var result_2A = 'some_text_for_test'.endsWith('test');    //應回傳true
    var result_2B = 'some_text_for_test'.endsWith('error');   //應回傳false
    
    message += 'endsWith result_2A : ' + result_2A + '</br>';
    message += 'endsWith result_2B : ' + result_2B + '</br>';
    
    var result_3A = 'some_text_for_test'.contains('for');     //應回傳true
    var result_3B = 'some_text_for_test'.contains('error');   //應回傳false

    message += 'contains result_3A : ' + result_3A + '</br>';
    message += 'contains result_3B : ' + result_3B + '</br>';
    
    $('#div1').html(message);
});



//判斷字串開頭是否為指定的字
//回傳: bool
String.prototype.startsWith = function(prefix)
{
    return (this.substr(0, prefix.length) === prefix);
}

//判斷字串結尾是否為指定的字
//回傳: bool
String.prototype.endsWith = function(suffix)
{
    return (this.substr(this.length - suffix.length) === suffix);
}

//判斷字串是否包含指定的字
//回傳: bool
String.prototype.contains = function(txt)
{
    return (this.indexOf(txt) >= 0);
}

<input type="button" id="test" value="test" />
<div id="div1"></div>