Array.concat vs Array.push

medini_1024169437

You may have seen plenty of scripts in this forum or elsewhere workingwith arrays. Some of them use the push() function, other use concat() (see push API doc on w3school and concat API doc). The fundamental difference is that push modifies an existing array while concat() returns a new array.

An example:

var a = ["A", "B"];
a.push("C");

alert(a.join(",")); // this will give A,B,C

An example with concat

var a = ["A", "B"];
a.concat("C");

alert(a.join(",")); // this will give A,B

// correct usage:
bar b = a.concat("C");

alert(b.join(",")); // this will give A,B,C

So you can use concat in places you do not want to modify the original array and push if you want.

Another nice thing with both methods is that they accept multiple arguments and they accept arrays as well as single elements!

var a = ["A"];

a.push("B", "C", ["D"]);

alert(a.join(",")); // this will give A,B,C,D

Happy Scripting

Jan

medini_1024169437

Note that we figured a limitation of the Rhino JS engine that is included with medini (1.7.5). Seems that concatenating native JS arrays works nice but when concatenating Java arrays, the result is not ok, see https://github.com/mozilla/rhino/issues/219 for details. So what does that mean: in simple terms the following code works:

['a', 'b'].concat(['c', 'd']) // results in ['a', 'b', 'c', 'd']

But this does not work:

// Assume we have a list ['c', 'd'] then
['a', 'b'].concat(list.toArray()) // results in ['a', 'b', ['c', 'd']] which is unexpected

We will try to upgrade to a newer version of the engine in one of the next major releases (but not 2023 R1). 

Happy Scripting

Jan