When looking to iterate through an array with the values [8,7,6,5,4], some may wonder why a for loop using the length of 5 continues to function even though there is no element at index 5 in the array.
for(let i=array.length;i>=0;i++){
//do something
}
While it would be technically correct to deduct 1 from the length value, this code still manages to work effectively.
Not quite there yet. Here's what you need to do:
i, you should decrease it,array.length-1.Try this instead:
for (let i = array.length-1; i >=0 ; i--) {
In JavaScript, arrays are not restricted to their declared size, which means that accessing an empty position will result in receiving undefined. For instance, when attempting to access array[5], the output will be undefined rather than throwing an ArrayIndexOutOfBoundsException like it would in Java.
Furthermore, when iterating through the array in reverse, it is important to decrement i using i-- instead of incrementing it.
Here is why:
const array = [1,2,3,4];
for(let i=10;i>=0;i--){
console.log(array[i]);
}You have the freedom to use a for loop with any conditions you desire in JavaScript. In this language, everything is treated as an object, including arrays. When trying to access a property that doesn't exist in an object using [], it will return undefined.
for(let index=array.length-1;index>=0;index--){
//perform a task
}
Make sure to assign the variable index to the length of the array minus one since array indexing starts at zero. Then, decrement index by one every time the loop iterates (using index--)
Your code is functional, but it may run for an extended period until the number overflows into negative territory. Consider adding a console.log(index) statement within your loop to observe this behavior (it could potentially freeze Chrome if done within the inspector)
When it comes to arrays, their length is not simply determined by the number of elements in them. Instead, the length of an array is based on the maximum index present in that array, especially for sparse arrays.
For instance:
let a = [];
a[10] = 1;
console.log(a.length);
console.log(a);In this case, the length of array 'a' is 11 (ranging from index 0 to 10), even though there are instances where some indices have values of undefined.
Interestingly, setting the last value to undefined doesn't impact the length as long as there is still a reference to undefined in that position.
let a = [];
a[9] = 1;
a[10] = 1;
console.log(a.length);
a[10] = undefined
console.log(a.length);Even using the delete method to remove elements won't alter the array's length property.
let a = [];
a[9] = 1;
a[10] = 1;
console.log(a.length);
delete a[10];
console.log(a.length);The only way to truly change the length of an array is by creating a new array containing a subset of the original one:
let a = [];
a[9] = 1;
a[10] = 1;
console.log(a.length);
console.log(a);
a = a.slice(0,9);
console.log(a.length);
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