Format number in thousands separators with jq json cli

Question

Given {"a": 1234567890}, I want 1,234,567,890 in the result, how this can be done with jq

echo '{"a": 1234567890}' | jq '.a | FORMAT?'

Thanks for @peak's answer, the solution is

echo '{"a": 1234567890}' | jq -r 'def h: [while(length>0; .[:-3]) | .[-3:]] | reverse | join(","); .a | tostring | h'
//-> 1,234,567,890

Answer 1

Here's an idiomatic one-liner definition:

def h: tostring | [while(length>0; .[:-3]) | .[-3:]] | reverse | join(",");

Example

12, 123, 1234, 12345678 | h

Output (using -r option):

12
123
1,234
12,345,678