[list].length
Since our collections of data may change while the app is running, we might need to know how many items are currently in a list (array). length will tell us how big the array is. Even if some of the elements in the array are empty strings or zero, they are counted by length.
In addition to the array variable name, items in your array are numbered with an index. The first element in an array is has index 0 and the second had index 1 and so on. As a result the last index is always one less than the length of the array.
Examples
Example: Pick a Day
Pick a random weekday and the last weekday.
// Pick a random weekday and the last weekday.
var weekDays = ["Monday","Tuesday","Wednesday","Thursday","Friday"];
var randomDayIndex=randomNumber(0,weekDays.length-1);
var lastDayIndex=weekDays.length-1;
console.log("Random weekday is " + weekDays[randomDayIndex]);
console.log("Last weekday is " + weekDays[lastDayIndex]);
Example: Make Change
Find the minimum number of coins to make change.
// Find the minimum number of coins to make change.
var coinValues = [1,5,10,25];
var coinCounts = [0,0,0,0];
var changeAmount = promptNum("How much change must I give you?");
while (changeAmount>0) {
for (var i=coinValues.length-1; i>=0; i--) {
var currentCoin=coinValues[i];
while (changeAmount>=currentCoin) {
changeAmount=changeAmount-currentCoin;
coinCounts[i]++;
}
}
}
console.log(coinCounts);
Syntax
[list].length
Parameters
| Name | Type | Required? | Description |
|---|---|---|---|
| list | variable name | The variable name of the list (array) you want to know the length of. |
Returns
Tips
- Off-by-one errors are very common when referencing array elements. Always pay attention to making sure you start at zero and end one less than the length of the array.
Found a bug in the documentation? Let us know at support@code.org.
