When a value should keep its name and identity, const prevents accidental reassignment. Declare it with an initial value; later assignment of a new value throws an exception. Use meaningful names such as MAX_RONIN_COUNT instead of unexplained numeric literals. section 5.5.1 section 5.5
Keep the key distinction in mind:
- const protects the binding from reassignment; it does not freeze an object or array it refers to. Properties can be added to an object, and an array can be changed with push. section 5.5.1
- const is block-scoped, like let. Variables declared with either keyword belong to their closest environment, while var ignores blocks. section 5.5.2
try{
firstConst = "ninja";
fail("Shouldn't be here");
} catch(e){
pass("An exception has occurred");
}
See the reassignment attempt that triggers an exception. section 5.5.1
secondConst.weapon = "wakizashi";
assert(secondConst.weapon === "wakizashi",
"We can add new properties");
See an object referenced by const gain a property without reassignment. section 5.5.1
const thirdConst = [];
assert(thirdConst.length === 0, "No items in our array");
thirdConst.push("Yoshi");
assert(thirdConst.length === 1, "The array has changed");
See an array referenced by const change when an item is pushed. section 5.5.1
