July 12, 2021 javascript
Strings becoming numbers in dates I was trying to add a number of years to a Date in JavaScript.
Should be easy except I forgot the cardinal rule of accepting user input: check it!
I was getting the number of years as an ‘integer’ via an API, but of course it turned out to be a string that looked like an integer.
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$ let d1 = new Date (2021 ,07 ,12 );
undefined
$ let years = 2 ;
undefined
$ let years_string = "2" ;
undefined
$ d1.getFullYear() + years;
2023 // Expected...
$ d1.getFullYear() + years_string;
"20212" // Oh brother...
$ let d2 = new Date (d1);
undefined
$ d2.getFullYear();
2021
$ d2.setFullYear(d2.getFullYear() + years);
1691820000000
$ d2
Date Sat Aug 12 2023 00 : 00 : 00 GMT- 0600 (Mountain Daylight Time)
$ d3 = new Date (d1);
Date Thu Aug 12 2021 00 : 00 : 00 GMT- 0600 (Mountain Daylight Time)
$ d3.setFullYear(d3.getFullYear() + years_string);
575681234400000 // Yeah, the math breaks...
$ d3
Date Wed Aug 12 20212 00 : 00 : 00 GMT- 0600 (Mountain Daylight Time)
// wait...the year 20212?!
It’s embarrassing how long it took me to spot that extra digit on the year!
How did I solve this issue?
A simple conversion fixed it:
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let years = parseInt (the_value_from_the_api);