Array concatenation

JavaScript

a1 = [0,1,2]
a2 = [1,2,23,6]
a3 = [78,76,2]
a4 = [456,2,45,2]
a5 = [123,-6,9]
    
var output = [];
for(var i = 1; window['a'+i]; i++){
    output = output.concat(window['a'+i]);
}

document.write(output);
console.log(output);