Operands must both be
numbers or strings in addition expressions JS-0377
Anti-pattern
6 months ago
—
6 months old
Operands to the
+ operator should be both numbers or both strings21 const app = fastify(fastifyOptions);
22
23 // Logger middleware for fastify instance (logs to console)
24 logger.info("\n\nEnvironment details: " + consoleOutput);25
26 routes(app);
27
Description
It is recommended to use operands of the same type while adding values as mismatched operand types might result in unexpected output.
When doing addition with operands of different types, the output sometimes results in simple concatenation instead of addition.
1 + '2'
While the user may expect this to result in 3 (by integer addition) it will instead result in '12' (by string concatenation) .
Bad Practice
var foo = '5.5' + 5;
var foo = 1n + 1;
Recommended
var foo = parseInt('5.5', 10) + 10;
var foo = 1n + 1n;