7.5 Adding and Deleting Array Elements
We’ve already seen the simplest way to add elements to an array: just assign values to new indexes:
a =  // Start with an empty array.
a = "zero"; // And add elements to it.
a = "one";
You can also use the push() method to add one or more values to the end of an array:
7.5 Adding and Deleting Array Elements | 145
a = ; // Start with an empty array a.push("zero") // Add a value at the end. a = ["zero"] a.push("one", "two") // Add two more values. a = ["zero", "one", "two"]
Pushing a value onto an array a is the same as assigning the value to a[a.length]. You can use the unshift() method (described in §7.8 ) to insert a value at the beginning of an array, shifting the existing array elements to higher indexes.
You can delete array elements with the delete operator, just as you can delete object properties:
a = [1,2,3]; delete a; // a now has no element at index 1 1 in a // => false: no array index 1 is defined a.length // => 3: delete does not affect array length
Deleting an array element is similar to (but subtly different than) assigning undefined to that element. Note that using delete on an array element does not alter the length property and does not shift elements with higher indexes down to fill in the gap that is left by the deleted property. If you delete an element from an array, the array becomes sparse.
As we saw above, you can also delete elements from the end of an array simply by setting the length property to the new desired length. Arrays have a pop() method (it works with push()) that reduces the length of an array by 1 but also returns the value of the deleted element. There is also a shift()method (which goes with unshift()) to remove an element from the beginning of an array. Unlike delete, the shift() method shifts all elements down to an index one lower than their current index. pop() and shift() are covered in §7.8 and in the reference section.
Finally, splice() is the general-purpose method for inserting, deleting, or replacing array elements. It alters the lengthproperty and shifts array elements to higher or lower indexes as needed. See §7.8 for details.欢迎转载,转载请注明来自一手册:http://yishouce.com/book/1/27654.html