Requires that private members are marked as readonly
if they're never modified outside of the constructor.
This rule enforces that private members are marked as readonly
if they're never modified outside of the constructor.
Member variables with the privacy private
are never permitted to be modified outside of their declaring class.
If that class never modifies their value, they may safely be marked as readonly
.
Examples of code for this rule:
class Container {
// These member variables could be marked as readonly
private neverModifiedMember = true;
private onlyModifiedInConstructor: number;
public constructor(
onlyModifiedInConstructor: number,
// Private parameter properties can also be marked as readonly
private neverModifiedParameter: string,
) {
this.onlyModifiedInConstructor = onlyModifiedInConstructor;
}
}
class Container {
// Public members might be modified externally
public publicMember: boolean;
// Protected members might be modified by child classes
protected protectedMember: number;
// This is modified later on by the class
private modifiedLater = 'unchanged';
public mutate() {
this.modifiedLater = 'mutated';
}
}
This rule, in its default state, does not require any argument.
You may pass "onlyInlineLambdas": true
as a rule option within an object to restrict checking only to members immediately assigned a lambda value.
{
"@typescript-eslint/prefer-readonly": ["error", { "onlyInlineLambdas": true }]
}
Example of code for the { "onlyInlineLambdas": true }
options:
class Container {
private onClick = () => {
/* ... */
};
}
class Container {
private neverModifiedPrivate = 'unchanged';
}
- TSLint: 'prefer-readonly'
- ✅ Recommended
- 🔧 Fixable
- 💭 Requires type information