It's considered a good practice to avoid using eval() in JavaScript. There are security and performance implications involved with doing so. However, there are some other ways to pass a string and have it interpreted as JavaScript code that have similar concerns.

One of the ways is by using setTimeout(), setInterval() or execScript() (Internet Explorer only), all of which can accept a string of JavaScript code as their first argument. For example:

setTimeout("alert('Hi!');", 100);

This is considered an implied eval() because a string of JavaScript code is passed in to be interpreted. The same can be done with setInterval() and execScript(). Both interpret the JavaScript code in the global scope. For both setTimeout() and setInterval(), the first argument can also be a function, and that is considered safer and is more performant:

setTimeout(function() {
    alert("Hi!");
}, 100);

Therefore, the best practice is to always use a function for the first argument of setTimeout() and setInterval() (and avoid execScript()).

Bad Practice

setTimeout("alert('Hi!');", 100);
setInterval("alert('Hi!');", 100);
execScript("alert('Hi!')");
window.setTimeout("count = 5", 10);
window.setInterval("foo = bar", 10);

Recommended

setTimeout(function() {
    alert("Hi!");
}, 100);

setInterval(function() {
    alert("Hi!");
}, 100);

References

KOSASIH / SilkRoad

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