Global Object API: parseInt()

parseInt() parses a string and returns an integer.

• it is a global function

WHEN given a numeric string

• THEN converts it to an integer
• AND a radix=16 THEN converts to an integer applying the radix (like hexadecimal)
• AND a radix=9 THEN converts to an integer applying the radix
• AND a radix=0 THEN converts to an integer assuming radix=10
• AND the string starts with 0x THEN converts to an integer assuming radix=16
• AND the string starts with 0X THEN converts to an integer assuming radix=16

WHEN given a NOT-numeric string (it will be tried to be converted to a string)

• a string starting with numbers THEN converts containing the leading numbers only
• a string starting with -F (a hexadecimal number) AND radix=16 THEN returns -15
• a string, a word made of letters only THEN returns NaN (not a number)
• an empty object literal THEN returns NaN
• an empty array THEN returns NaN
• an array with [123,456] THEN converts it to a string and then to an integer

Links

spec docs The very first version of the spec defining `parseInt`, the ES1 spec.
spec docs A later, newer version of the spec text for `parseInt`, from ES10.
mdn docs The description of `parseInt()` on MDN, probably best to read.
announcement Announcement of this kata on twitter.