Description
When using the +/- operator with strings and numbers.
There are many traps here, and things can go wrong.
e.g.
let result = '5' + 3;
console.log(result); // '53' - String concatenation
let result = '5' - 3;
console.log(result); // 2 - The string is converted to a number
result = 3 + '5';
console.log(result); // '35' - Still string concatenation
let result = '10' - 3;
console.log(result); // 7 - The string '10' is converted to the number 10
result = '5' - '2';
console.log(result); // 3 - Both strings are converted to numbers and then subtractedI know, no one would write code like this in the real world
But there will be the following situation
function foo() {
// ...other logic
return "5"
}
// ... other logic
const bar = foo() + 5 // ❌We should check that left and right expression are of the same type to avoid implicit conversion.
It is feasible when we can infer its type, skip check when found any/unknown/never.
There is no possibility of false positives
Fail
Plus operator:
const foo = "5" // numberic
// ... other logic
const bar = foo + 5 // ❌function foo() {
return "5"
}
// ... other logic
const bar = foo() + 5 // ❌Minus operator:
const foo = "10"
// ...other logic
const bar = foo - 5 // ❌Type Annotation:
let foo: string
// ...other logic
const bar = foo - 5 // ❌let foo = (): string => {}
// ...other logic
const bar = foo() - 5 // ❌function foo (bar: string) {
bar - 5 // ❌
}Pass
const foo = "5"
// ... other logic
const bar = Number(foo) + 5 // ✅function foo() {
return "5"
}
// ... other logic
const bar = Number(foo()) + 5 // ✅Minus operator:
const foo = "10"
// ...other logic
const bar = Number(foo) - 5 // ✅Proposed rule name
no-implicit-conversion
Additional Info
No response
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