I want to define an array in a line of the program, for example, as follows:
var a = [2,5];
//In the next steps, I want to increase the array elements as follows:
a[0] += 2;
a[1] += 2;
//And I want the array to increase intermittently at the output of the program, as follows:
a = [4,7]
a = [6,9]
a = [8,11]
//....
But in reality this does not happen because in the first line of the program, the array is defined again and again.
And the output is always as follows: a = [4,7];
Is there a way to initialize the a array as [2,5] only once?
There are many ways to do this.
let a = [2,5];
for (let i=0;i<5;i++) {
a=a.map(element=>element+2);
console.log(a);
}
Using a nested function/closure as shown in Lonnie Best's answer
Or you can also use a generator function:
function * arrayIncreaser(initialArray, num) {
let a = initialArray;
while (true) {
a = a.map(element=>element+num)
yield a;
}
}
const increaser = arrayIncreaser([2,5],2)
console.log(increaser.next().value);
console.log(increaser.next().value);
console.log(increaser.next().value);
Here, I use a closure. The array is created once and modified each time you call increase():
function createIncreaseFunction()
{
const a = [2,5];
function increase()
{
a[0] += 2;
a[1] += 2;
return a;
}
return increase;
}
let increase = createIncreaseFunction();
console.log(increase()); // [4,7]
console.log(increase()); // [6,9]
console.log(increase()); // [8,11]
// increase() modifies the values in the array,
// but the same array is returned each time:
console.log(increase() === increase()); // true