Say I have an array definition
var array = [
"One",
"Two",
"Three",
]
...but I only want "three" to be added when another variable is true.
var array = [
"One",
"Two",
(addThree ? "Three" : undefined),
]
The issue is, if addThree is false, then the array becomes ["One","Two",undefined] when I just want it to be ["One","Two"].
You could take Array#concat and a conditional (ternary) operator ?: for checking addThree and take the value or an empty array.
The empty array does not change the length of the returned array.
var addThree = false,
array = ["One", "Two"].concat(addThree ? "Three" : []);
console.log(array);There are number of ways to do this.
1. Using spread operator (...)
var addThree=false;
const array = [
"One",
"Two",
...(addThree ? ['Three'] : []),
]
console.log(array);spread operator (...) for Array literals does nothing if its operand is an empty Array.Using the spread operator in this manner leads to slightly cryptic code.
2. Another Alternative is to conditionally insert either elements or undefineds and to then filter the latter values out
var addThree=true;
var array = [
"One",
"Two",
(addThree ? 'Three' : undefined)
].filter(Boolean);
console.log(array);3. An elegant and self-descriptive solution is to use push() to construct the Array:
var addThree=true;
const array = [];
array.push('One');
array.push('Two');
if (addThree) {
array.push('Three');
}
console.log(array);
Initialize it with static items that aren't going to change, and then conditionally add the third if your condition is true:
var array = [
"One",
"Two",
];
if (addThree) {
array.push("Three");
}
...(addThree ? ['Three'] : [])