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Objects allow us to create a single entity that stores data items by key, and arrays allow us to gather data items into an ordered collection.But when we pass those to a function, it may need not an object/array as a whole, but rather individual pieces.
If there are fewer values in the array than variables in the assignment, there will be no error.
Absent values are considered undefined: We have an existing object at the right side, that we want to split into variables.
For instance, a single element with a large index gives a big length: .
To evade such surprises, we usually use square brackets, unless we really know what we’re doing.
An example of how the array is destructured into variables: // we have an array with the name and surname let arr = ["Ilya", "Kantor"] // destructuring assignment // sets first Name = arr // and surname = arr let [first Name, surname] = arr; alert(first Name); // Ilya alert(surname); // Kantorlet [name1, name2, ...rest] = ["Julius", "Caesar", "Consul", "of the Roman Republic"]; alert(name1); // Julius alert(name2); // Caesar // Note that type of `rest` is Array.
alert(rest); // Consul alert(rest); // of the Roman Republic alert(rest.length); // 2, just make sure it has three dots before it and goes last in the destructuring assignment.
is a special syntax that allows us to “unpack” arrays or objects into a bunch of variables, as sometimes that’s more convenient.
Destructuring also works great with complex functions that have a lot of parameters, default values, and so on.
Methods that work with the end of the array: let fruits = ["Banana"] let arr = fruits; // copy by reference (two variables reference the same array) alert( arr === fruits ); // true arr.push("Pear"); // modify the array by reference alert( fruits ); // Banana, Pear - 2 items now…But what makes arrays really special is their internal representation.
The engine tries to store its elements in the contiguous memory area, one after another, just as depicted on the illustrations in this chapter, and there are other optimizations as well, to make arrays work really fast.