javascript - Modifying one array modifies another one I made from it -

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this question has answer here:

var allcoords = [{ x: 2, y: 3 }, { x: 3, y: 4 }]; var emptyspaces = allcoords;  emptyspaces.splice(0, 1); console.log(allcoords.length); console.log(emptyspaces.length);

i not understand why both of these output "1". why original array, allcoords being modified, when want second one, emptyspaces edited?

modify code this:

(function testing() {     var allcoords = [];     var emptyspaces = allcoords.slice();      emptyspaces.push({         x: 1,         y: 2     });     console.log(allcoords.length);     console.log(emptyspaces.length); }());

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