Execute JavaScript code stored as a string

You can execute it using a function. Example:

var theInstructions = "alert('Hello World'); var x = 100";

var F=new Function (theInstructions);

return(F());

The eval function will evaluate a string that is passed to it.

But the use of eval can be dangerous, so use with caution.

Edit: annakata has a good point -- Not only is eval dangerous, it is slow. This is because the code to be evaluated must be parsed on the spot, so that will take some computing resources.

Use eval().

W3 Schools tour of eval. Site has some usable examples of eval. The Mozilla documentation covers this in detail.

You will probably get a lot of warnings about using this safely. do NOT allow users to inject ANYTHING into eval() as it is a huge security issue.

You'll also want to know that eval() has a different scope.

Try this:

  var script = "<script type=\"text/javascript\"> content </script>";
  //using jquery next
  $('body').append(script);//incorporates and executes inmediatelly

Personally I didnt test it, but seems to work.

Use eval as below. Eval should be used with caution, a simple search about "eval is evil" should throw some pointers.

function ExecuteJavascriptString()
{
    var s = "alert('hello')";
    eval(s);
}

eval(s);

But this can be dangerous if you are taking data from users, although I suppose if they crash their own browser thats their problem.

Checked this on many complex and obfuscated scripts:

var js = "alert('Hello, World!');" // put your JS code here
var oScript = document.createElement("script");
var oScriptText = document.createTextNode(js);
oScript.appendChild(oScriptText);
document.body.appendChild(oScript);

A bit like what @Hossein Hajizadeh alerady said, though in more detail:

There is an alternative to eval().

The function setTimeout() is designed to execute something after an interval of milliseconds, and the code to be executed just so happens to be formatted as a string.

It would work like this:

ExecuteJavascriptString(); //Just for running it

function ExecuteJavascriptString()
{
    var s = "alert('hello')";
    setTimeout(s, 1);
}

1 means it will wait 1 millisecond before executing the string.

It might not be the most correct way to do it, but it works.

eval should do it.

eval(s);

Not sure if this is cheating or not:

window.say = function(a) { alert(a); };

var a = "say('hello')";

var p = /^([^(]*)\('([^']*)'\).*$/;                 // ["say('hello')","say","hello"]

var fn = window[p.exec(a)[1]];                      // get function reference by name

if( typeof(fn) === "function") 
    fn.apply(null, [p.exec(a)[2]]);                 // call it with params

eval(s);

Remember though, that eval is very powerful and quite unsafe. You better be confident that the script you are executing is safe and unmutable by users.

New Function and apply() together works also

var a=new Function('alert(1);')
a.apply(null)

If you want to execute a specific command (that is string) after a specific time

function ExecStr(cmd, InterVal) {
    try {
        setTimeout(function () {
            var F = new Function(cmd);
            return (F());
        }, InterVal);
    } catch (e) { }
}
window.ExecStr = ExecStr;