Question

I have an html div that is of a fixed size and an additional HTML input box that is used to input text. This text is then displayed in the div.

I want the text to always be centred and always be the largest size possible for the number of characters in the string.

I have come up with a working prototype but it doesn’t work too well. The text is not always correctly sized.

function bindText(readElement, writeElement, extra){   
    //the text from the input form triggered by onkeyup event
    var textStr = document.getElementById(readElement).value;

    //the div to write the text to 
    var element = document.getElementById(writeElement);

    //the major part of the function that I have just brute forced to try and work out
    if(textStr.length > 0){                        

        //check the length of the string
        if(textStr.length > 8 && textStr.length < 12){
             //set a the font size accordingly
             element.style.fontSize = 150;
        }

        //same again    
        if(textStr.length >= 12 && textStr.length < 16){
            element.style.fontSize = 120;
        }

        if(textStr.length >= 16 && textStr.length < 20){
            element.style.fontSize = 100;
        }

        if(textStr.length >= 20 && textStr.length < 25){
            element.style.fontSize = 80;
        }

        if(textStr.length >= 25 && textStr.length < 32){
            element.style.fontSize = 55;
        }

        if(textStr.length >= 32 && textStr.length < 40){
            element.style.fontSize = 50;
        }

        if(textStr.length >= 40 && textStr.length < 50){
            element.style.fontSize = 45;
        }

        if(textStr.length >= 76){
            element = textStr.splice(0, 75);
        }
       }
   }

Is there a more elegant solution to get more consistent results.?

Thanks in advance

Answer 1

As I can see in your approximation of dependence between font size and length of the text:

I made interpolation for this in form:

and you can see the results of this with parameters:

Now you can replace all your if and else if by one formula for font size h calculation and couple min(h, max_font_size) and max(min_font_size, h) for setting of the font minimal and maximum size.

function bindText(readElement, writeElement, extra){   
    var textStr = document.getElementById(readElement).value;
    var element = document.getElementById(writeElement);
    var x, h;

    x = textStr.length;
    h = Math.exp(-0.1 * x + 6) + 38;
    h = Math.min(h, 120);
    h = Math.max(h, 45);

    element = textStr.splice(0, 75);// as you wish and it is not my business why %)
    element.style.fontSize = h;

    return (0);
}