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<meta charset="UTF-8">
<title>JavaScript const example</title>
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<script>
const a = 10;
console.log("Constant a: ", a); // a value 10
const b; // weird, const can define without initial value,
console.log("Constant b: ", b); // automatic assign 'undefined'
//const a = 20; // throw TypeError 'a' already been declared
//var a = 20; // throw TypeError 'a' already been declared
// 'a' is already used as a constant can not declare as a variable
a = 20; // Define 'a' variable without var keyword, can't throw error
console.log("a without var:", a);
const c = 20; // Define and initializing 'c' constant variable
const d = b; // Define 'd' constant variable, initialize constant 'c'
console.log("Constant c: ", c);
console.log("Constant d: ", d);
const obj = {"a": "A", "b": "B"}; // Define and initializing constant object
console.log("Constant Object:", obj);
console.log("Constant obj.a:", obj.a);
//var obj = 10; // throw TypeError 'obj' already been declared
obj.a = "AA"; // 'a' key, try to reassign
console.log("Reassign after Object:", obj); // Object {a: "AA", b: "B"}
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