argument concatenation in a recursive function

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Wahid Polin

The example is from the book "dom scripting" - jeremy keith.

function moveElement(elementID,final_x,final_y,interval) { 
if (!document.getElementById) return false; 
if (!document.getElementById(elementID)) return false; 
var elem = document.getElementById(elementID); 
var xpos = parseInt(elem.style.left); 
var ypos = parseInt(elem.style.top); 
if (xpos == final_x && ypos == final_y) { 
return true; 
} 
if (xpos < final_x) { 
xpos++; 
} 
if (xpos > final_x) { 
xpos--; 
} 
if (ypos < final_y) { 
ypos++; 
} 
if (ypos > final_y) { 
ypos--; 
} 
elem.style.left = xpos + "px"; 
elem.style.top = ypos + "px"; 
var repeat = "moveElement('"+elementID+"',"+final_x+","+final_y+","+interval+")"; 
movement = setTimeout(repeat,interval);
}

I don't understand why there's so many concatenation in this line

var repeat = "moveElement('"+elementID+"',"+final_x+","+final_y+","+interval+")";

Matt

It's because var repeat is actually a string representation of a function call, rather than a function itself.

To do the same thing in code (not using a string) you'd do something like this:

    var repeat = function() { moveElement(elementId, final_x, final_y, interval); }
    movement = setTimeout(repeat, interval);

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에서 수정2021-06-1

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