when we define an array as constant in javascript does it mean that array cannot shrink or enlarge and have a constant size, or, does it mean that all the elements in an array are constant and you cannot change their value.
handleClick(i) { const squares = this.state.squares.slice(); squares[i] = 'X'; this.setState({squares: squares}); } in the above code.
Declaring a variable as const only means that you cannot assign a new value to that variable once a value has been assigned:
const array = []; array = []; // Not allowed: assignment to constant variable Declaring an array as const has no bearing on what you can do with the contents of the actual array:
const array = []; array.push("something"); // Allowed: add value to array array[0] = "or other"; // Allowed: replace value in array array.length = 0; // Allowed: change array size 
const keyword is simply used to declare a constant reference to an object. This reference cannot be made to refer to something else but the object referred to can still be mutated.