Can javascript generate executable javascript code?

Question

This is a sample javascript code to alert the user if he clicks shift + 1 (or 2,3...9)

But as you see this code is almost the same.

a = window.event.keyCode;

var b = window.event.shiftKey

if (a == 49 && b) {
    alert(document.getElementById('alert1').length)
}
if (a == 50 && b) {
    alert(document.getElementById('alert2').length)
}
if (a == 51 && b) {
    alert(document.getElementById('alert3').length)
}
if (a == 52 && b) {
    alert(document.getElementById('alert4').length)
}
if (a == 53 && b) {
    alert(document.getElementById('alert5').length)
}
if (a == 54 && b) {
    alert(document.getElementById('alert6').length)
}
if (a == 55 && b) {
    alert(document.getElementById('alert7').length)
}
if (a == 56 && b) {
    alert(document.getElementById('alert8').length)
}
if (a == 57 && b) {
    alert(document.getElementById('alert9').length)
}

Is there any javascript (it can be jQuery) code (using for(){} method or something else) that will do the same job by writing less code and the other code to be generated by the browser and executed when is required?

'alertX' are all strings. You can create then dynamically from the value of a. Give it a go. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Dec 30, 2012 at 17:53
possible duplicate of javascript - check a range of numbers in if statement with regex — Roko C. Buljan
– Roko C. Buljan, Commented Dec 30, 2012 at 18:01

AmShaegar · Accepted Answer · 2012-12-30 17:56:07Z

9

You should not create executable Javascript but review your code.

Repetitive code can most times be written as a loop or in your case by math.

if(a < 58 && a > 48 && b) {
  alert(document.getElementById('alert'+(a-48)).length)
}

answered Dec 30, 2012 at 17:56

AmShaegar

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Comments

schematic · Accepted Answer · 2012-12-30 18:25:51Z

2

You probably don't really want code generation + execution, that can get pretty dangerous.

All you need is a little DRYing of your code:

var ALERT_KEYCODE_OFFSET = 48;
var alertIndex, alertId;
if (a >= 49 && a <= 57 && b)
{
    alertIndex = a - ALERT_KEYCODE_OFFSET;
    alertId = 'alert' + alertIndex;
    alert(document.getElementById(alertId).length);
}

edited Dec 30, 2012 at 18:25

answered Dec 30, 2012 at 17:58

schematic

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5 Comments

Paul S. Over a year ago

Using var in if makes me cry. It makes following the scope of variables much more tedious.

schematic Over a year ago

So it's less tedious if everything's just global? OK. Is there a special scoping rule for "if" that I'm not aware of?

schematic Over a year ago

Eh @PaulS., my bad. Now I know things. I hate you JavaScript. For those who don't know, see stackoverflow.com/questions/500431/javascript-variable-scope

Paul S. Over a year ago

I mean it's less tedious if you set the var before the if, not inside it. if blocks don't have their own scope unless you can use JavaScript 1.7's let, any var gets hoisted upwards to the beginning of the scope. This means if you're trying to find if/which scope a var is declared, it can get confusing if written like this. EDIT Yup, non-block-scoping is one of the many quirks of JavaScript.

schematic Over a year ago

Yeah, I had this foolish idea that there was such a thing as block scope for var (without using let). I mean, it looks like it should. Thanks for showing me otherwise!

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