The left-hand side of an arithmetic operation must be of type 'any', 'number' or an enum type
Solution 1:
Here is another example of this error occurring that might help people.
If you're using typescript and trying to compute the difference between dates (In my case I was attempting to use ISO string from database):
new Date("2020-03-15T00:47:38.813Z") - new Date("2020-03-15T00:47:24.676Z")
TypeScript Playground
It will show the error.
However, this same exact code works if you put it in the browser console or other node environment
new Date("2020-03-15T00:47:38.813Z") - new Date("2020-03-15T00:47:24.676Z")
14137
I may be wrong, but I believe this works due to the - operator implicitly using valueOf on each of it's operands. Since valueOf on Date returns a number the operation works.
However, typescript doesn't like it. Maybe there is a compiler option for this is forcing this constrain and I'm not aware.
new Date().valueOf()
1584233296463
You can fix by explicitly making the operands number (bigint) types so the - works.
Fixed Example
new Date("2020-03-15T00:47:38.813Z").valueOf() - new Date("2020-03-15T00:47:24.676Z").valueOf()
TypeScript Playground
Solution 2:
Number should be lowercase: number.
- See sample on Playground
- Documentation for basic types
Solution 3:
cleanest way I found:
const diff = +new Date("2020-03-15") - +new Date("2020-03-15")
https://github.com/microsoft/TypeScript/issues/5710