How to restrict number of character per line in textarea

I have one extJS TextArea. There i want to restrict my character to 15 character in line each line and total number of line should not more than 10.

What I am tring to do here is

function(){
    var myValue = this.getValue();
    var myValueData = myValue.split(/\r*\n/);
        myValueData.length = 10;    
}

Ideally it should ommit all the lines after line number 10, but not happening. Also How to restrict only upto 15 character per line.

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