For example the month is June 2020. I want to be able to go back by 12 months, and retrieve the date as June/July 2019.
let month_val = 6;
let year_val = 2020;
let n_val = 12;
let month_names = ["January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November", "December"
];
let date = new Date();
let end_month_text = month_names[month_val - 1];
end_month_text += " " + year_val;
date.setMonth(month_val); //set to month in URL
date.setMonth(date.getMonth() - n_val); //setting back by n_val months
let start_month_text = month_names[date.getMonth()];
start_month_text += " " + date.getFullYear();
console.log(start_month_text + " - " + end_month_text);The problem lies with the second to last line, date.getFullYear() returns the current real year (-12) not last year set back 12 months ago. How can I set the date back 12 months so when I attempt to date.getFullYear() I get one year ago?
The problem with using a Date as in the OP is that in setting the month, you may set it to a date that doesn't exist, e.g. on 31 July setting the date to June gives 31 June, which rolls over to 1 July. You can check and correct for those types of errors, but it's better to just avoid them.
If you just want to generate a 12 month date range based on whole months, you don't need to get that fancy. Given an end month and year, the start will be the month + 1 and year - 1, unless the start month is December in which case the end must be January of the same year, e.g.
// month is calendar month number, 1 == Jan
function getMonthName(month = new Date().getMonth() + 1) {
// Use a Date to get the month name
return new Date(2000, month - 1).toLocaleString('en',{month:'long'});
}
// month is end calendar month number
// year is end year
function getDateRange(month, year) {
// If month is 12, don't subtract 1 from year
return `${getMonthName(month+1)} ${year - (month == 12? 0 : 1)} - ` +
`${getMonthName(month)} ${year}`;
}
// Range ending June 2021
console.log(getDateRange(6, 2021)); // July 2020 - June 2021
// Range ending December 2021
console.log(getDateRange(12, 2021)); // January 2021 - December 2021
// Range ending January 2021
console.log(getDateRange(1, 2021)); // February 2020 - January 2021
// Range ending in current month and year
let d = new Date();
console.log(getDateRange(d.getMonth() + 1, d.getFullYear()));The getMonth function could use any language, or for just one language could be replaced with an array of month names.