Need help with RangeError

I'm trying to prepare animation of heatness spreading. But problem is that I can only calculate heat for matrixes with size 12x12x12. When I'm trying to use bigger values I receive: RangeError: execution timeout.

I'm trying to generate simulation on table (using hitTestResult from WoldMeshController).

createMatrix function creates a 3D array to store objects representing every cell and store it in global.matrix

_global.heatness is 3D array which stores only values of the heat (these ones are used to calculate heat in every step of algorithm)

global.heatnessSource_X/Y/Z are coords of heat source

Function for calculating heat for whole 3D matrix:

global.startVisualization = function() {

var centerOfScreenPos = new vec2(0.5, 0.5);
if (global.WorldMeshController.isInitialize) {
    var rayCastRes = global.WorldMeshController.getHitTestResult(centerOfScreenPos);
    if (!rayCastRes.isValid()) {
        return;
    } else if (rayCastRes.getClassification() == 4) {
        var pos = rayCastRes.getWorldPos();
        var substractValue = global.matrixShape/2 * 3.5;
        createMatrix(pos.x-substractValue, pos.y, pos.z-substractValue, global.matrixShape);

        global.heatness[global.heatnessSource_X][global.heatnessSource_Y][global.heatnessSource_Z] = global.heatnessValue;
        for (var t = 0; t < script.time; t++) {
                global.heatness = spreadHeatness(script.h, script.dt, script.e);
        } 
    } else {
        global.logToScreen("Wrong suface: " + rayCastRes.getClassification());
    }
}

}

Function to calculate heat in every algorithm step:

function spreadHeatness(h, dt, e) {
var newHeatness = global.heatness.map(function(arr) {
return arr.slice();
});

for (var x = 1; x < global.heatness.length-1; x++) {
    for (var y = 1; y < global.heatness.length-1; y++) {
        for (var z = 1; z < global.heatness.length-1; z++) {
            dx2 = e * ((global.heatness[x+1][y][z] - 2*global.heatness[x][y][z] + global.heatness[x-1][y][z]) / (h*h));
            dy2 = e * ((global.heatness[x][y+1][z] - 2*global.heatness[x][y][z] + global.heatness[x][y-1][z]) / (h*h)); 
            dz2 = e * ((global.heatness[x][y][z+1] - 2*global.heatness[x][y][z] + global.heatness[x][y][z-1]) / (h*h)); 

            var new_color = global.heatness[x][y][z] + dt * (dx2 + dy2 + dz2);

            if (x == global.heatnessSource_X && y == global.heatnessSource_Y && z == global.heatnessSource_Z) {                        
                new_color = new_color + global.heatnessValue;
            }
            newHeatness[x][y][z] = new_color;

        }
    }
}

return newHeatness;

}
So as I mentioned earlier, for matrixShape > 12 I'm getting RangeError: execution timeout. I do not know why, but I would like to generate simulations for much bigger 3D matrix. JS is not my main advantage so description of this error from documentation is not saying much to me.

This error is happing every time in different line, but always in spreadHeatness function.

I'll be glad for every help, Thanks!!!