Modify Dates in a certain format in an array of objects JavaScript

I am trying to modify the dates in an object in below format. Basically I want to first convert the string date into date format, then try to get the year and decide if it's 1st half of the year i.e. from 2023.01.01 to H1' 2023 or 2nd half of the year i.e. from 2023.07.01 to H2'2023 and then update the dates. Really appreciate your help Thanks

// Current Data set 

data = [{'description': 'halfyear', date: '2024.01.01'},
	{'description': 'halfyear', date: '2024.07.01'},
	{'description': 'halfyear', date: '2016.01.01'},
	{'description': 'halfyear', date: '2016.07.01'}
	]

// Expected Data 

data = [{'description': 'halfyear', date: 'H1\'2024'},
	{'description': 'halfyear', date: 'H2\'2024'},
	{'description': 'halfyear', date: 'H1\'2016'},
	{'description': 'halfyear', date: 'H2\'2016'}
	]

I have tried below but it doesn't seem to update correctly and override the values.

data.map(x=> {
 return x.formatted = 'H' + ' ' + new Date(x.date).getMonth() + 1 < 6 ? '1': '2' + new Date(x.date).getFullYear() + ''
})

Current Data- https://i.stack.imgur.com/jX9EK.png

Expected Result: https://i.stack.imgur.com/7tcMO.png

To avoid confusion while managing brackets and operator precedence I would recommend using template literals. Also you don't need to add to the month 1 since the math is already working (< 6).

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const data = [
    { 'description': 'halfyear', date: '2024.01.01' },
    { 'description': 'halfyear', date: '2024.07.01' },
    { 'description': 'halfyear', date: '2016.01.01' },
    { 'description': 'halfyear', date: '2016.07.01' }
];

// if you need a copy
const mapped = data.map(({date, description}) => {
    const [year, month] = date.split('.');
    return {
      description,
      date: `H${month < 6 ? 1 : 2}\'${year}`
    };
});

// if you need in-place transform
data.forEach(item => {
    const [year, month] = item.date.split('.');
    item.date = `H${month < 6 ? 1 : 2}\'${year}`;
});

console.log(JSON.stringify(mapped));

console.log(JSON.stringify(data));

<!-- end snippet -->

It's inefficient to parse the string to a Date just to call a method to get back the month value when it's available directly from the string. It's particularly problematic to use the built–in Date parser with an unsupported string format.

To modify the value of the date property based on the month, just parse out the month and see if it's < 7. E.g.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let data = [
 {'description': 'halfyear', date: '2024.01.01'},
 {'description': 'halfyear', date: '2024.07.01'},
 {'description': 'halfyear', date: '2016.01.01'},
 {'description': 'halfyear', date: '2016.07.01'}
];

let data2 = data.map(obj => {
  let [y, m, d] = obj.date.split(/\D/);
  return {...obj, date: `H${m < 7? 1: 2}'${y}`}; 
});

console.log(data2)

<!-- end snippet -->

PS

An issue in the OP is the following expression (looking at just the part up to and including the conditional expression):

'H' + ' ' + new Date(x.date).getMonth() + 1 < 6 ? '1': '2'

This is evaluated as:

('H' + ' ' + new Date(x.date).getMonth() + 1) < 6 ? '1': '2'

If new Date(x.date).getMonth() returns say 3, the comparison expression resolves to:

('H' + ' ' + 3 + 1) < 6

which evaluates to (noting that the addition operator + is evaluated left to right and since the first expression is a string, each subsequent expression is converted to string before being added):

'H 31' < 6

The less than operator < uses the abstract relational algorithm. It first converts the operands to primitive and if the result isn't two strings, converts them to numbers. toNumber('H 31') returns NaN, so now you have:

NaN < 6

This expression evaluates to undefined (step 4.d), regardless of the value returned by getMonth (an integer in the range 0 to 11 or NaN):

undefined ? '1' : '2'

Now the algorithm for the conditional operator ? : kicks in and calls toBoolean on the left hand side, which returns false:

false ? '1' : '2'

So the result will always be '2'.

To get the result you want, add some brackets to force the conditional expression to be evaluated without interference from the surrounding code:

'H' + ' ' + (new Date(x.date).getMonth() + 1 < 6 ? '1': '2') + new Date(x.date).getFullYear() + ''

An extra set of brackets might help with readability:

'H' + ' ' + ((new Date(x.date).getMonth() + 1) < 6 ? '1': '2') + new Date(x.date).getFullYear() + ''

This of course assumes that new Date(x.date) returns a valid Date, which, in the OP, it doesn't in some implementations.