asynchronous - Matrix multiplication implement in JavaScript -

i implement simple matrix multiplication in javascript for

var multipliction = function(matrixa,matrixb){     var result = [];     (var = 0;i < matrixa.length;i++){         result.push(new array());         (var j = 0;j < matrixb.length;j++)                 result[i].push(0);     }      (var = 0;i < matrixa.length;i++)         (var j = 0;j < matrixa[i].length ;j++)             for(var k = 0;k < matrixb[j].length;k++)                 result[i][j] += matrixa[i][k] * matrixb[k][j];     return result; }; 

but think runs async ,so if part takes long execute,it jump next , result is't trusted, what's way sure above code run synchronously ?