slice vs splice

slice and splice are common methods to get a sub-array of a given array.

Differences

  1. The signature of methods are different.
    array.slice(startingIndex, endingIndex);
    array.splice(startingIndex, length, ...items);
    While the first parameter are the same as each other indicating the starting index of removed elements, the second parameters aren't.
    The second parameter of slice and splice are the ending index and the number of sub items, respectively.
    With the splice method, it's possible to keep the items not to be removed from the original array by passing them to the last parameters.
  2. splice changes the original array, while slice doesn't.
    Given the array of numbers from 1 to 5:
    const array = [1, 2, 3, 4, 5];
    const sub = array.splice(2, 3);
    
    // The original array is modified
    array;      // [1, 2]
    sub;        // [3, 4, 5]
    Now, let's pass the same parameters to slice:
    const array = [1, 2, 3, 4, 5];
    const sub = array.slice(2, 3);
    
    // The original array isn't modified
    array;      // [1, 2, 3, 4, 5]
    sub;        // [3]

Tip

We can clone an array by ignoring the ending index:
const clone = arr => arr.slice(0);
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