Tslint: Ternary with null value marked as unused expression

[james-prado]

Bug Report

• __TSLint version__: 5.9.1
• __TypeScript version__: 2.7.2
• __Running TSLint via__: VSCode

TypeScript code being linted

onEnter = (e: KeyboardEvent) => {
    e.keyCode === 13 ? fetchData(url) : null;
};

with tslint.json configuration:

"no-unused-expressions": [true, "allow-fast-null-checks"],

Actual behaviour

Referring to the null value -[tslint] unused expression, expected an assignment or function call (no-unused-expression)

Expected behaviour

Allow ternary operations that evaluate to null

[giladgray]

@james-prado this behavior is completely expected. null; by itself is rejected with the same error. use an if statement for this pattern.

[godenji]

Ternary operator shorthand is a natural use case here, we don't care about the false case. In comparison if condition is just noise.

if (cond) {
  effect()
}

cond ? effect() : null