JavaScript ternary condition with date-CodePudding

Here I am getting true. I should get a false value instead.

let x = 2021;
let y = 12;

getMn = new Date(x,y).getMonth()

const date = new Date();
let xyz = (date.getMonth() <= getMn ) ? false : true;

console.log(xyz);

So here i dont understand why i am getting true value if i check in console by place 11 directly instead of date.getMonth ( 11 <= 0 ? false : true) then I am getting false then my question is why its returning me different results both the scenario

CodePudding user response：

Lets debug this by adding the following line:

console.log(getMn, date.getMonth());

This yields 0 11. The 0 is caused by the months being 0-indexed, so we'll need an 11 for December.

One more note, instead off () ? false : true we can simply revert the expressions with an !:

let x = 2021;
let y = 11;   // December

getMn = new Date(x,y).getMonth()

const date = new Date();
let xyz = !(date.getMonth() <= getMn )

console.log(getMn, date.getMonth());
console.log(xyz);

CodePudding user response：

Your expression is really 11 <= 0 ? false : true.

Since obviously 11 is not less or equal to 0 the latter part gets evaluated (after :), and so you get true.

BTW, the expression 11 <= 0 ? false : true is the same as 11 > 0 without any ternary.

CodePudding user response：

Well date.getMonth() is zero-based according to the documentation here -> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getMonth

So when you do date.getMonth() <= 11 ? false : true the condition is true so it returns false. If the condition is false then it will return true. And the getMn.getMonth() is like so 11 <= 0 which is false so it returns true. The ternary operator is like so: if the condition is true you return the condition after the "?" and if it is false you return the condition after the ":". Check this about the ternary https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator