Prototypes and funtions

This may be a little problem but I can’t figure out.
I try to set a prototype that controls a kind of vibrating movement for letters. These letters are inside of a mc called VE(vibr. effect)
and I type the code in the first frame of the mc timeline but doesn´t works.

this is the code

[FONT=courier new]MovieClip.prototype.vib = funtion();[/FONT]

[FONT=courier new]sx = this._x;[/FONT]
[FONT=courier new]sy = this._y;[/FONT]
[FONT=courier new]this._x = sx+(Math.random()*5);[/FONT]
[FONT=courier new]this._y = sy+(Math.random()*5);[/FONT]

[FONT=courier new]for (i=0; i<21; i++) {[/FONT]
[FONT=courier new] _root[“ve”+i].vib();[/FONT]
[FONT=courier new]}[/FONT]

If anyone can help I’d be grateful:

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