The basic of readonly property
In Type Script, you can make the object of the properties of an object read-only.
person.name = 21;
// → Cannot assign to ‘name’ because it is a read-only property.
⚠️① readonly is only at compile-time
In the compiled JavaScript code, the readonly declaration is removed, so it will not be detected as an error at runtime.
⚠️② readonly is not recursive.
readonly name: string;
readonly academicBackground: {
primarySchool: string
}
} = {
name: ‘Mike‘,
academicBackground: {
primarySchool: ‘School A‘
}
}
person.academicBackground.primarySchool = ‘School B‘
// You can change `person.academicBackground.primarySchool`
If you want to make it read-only, also you need to put readonly to primarySchool.
readonly name: string;
readonly academicBackground: {
readonly primarySchool: string
}
} = {
name: ‘Mike‘,
academicBackground: {
primarySchool: ‘School A‘
}
}
person.academicBackground.primarySchool = ‘School B‘
// → Cannot assign to ‘primarySchool’ because it is a read-only property.
Readonly
When the number of properties increases, adding readonly to each one becomes cumbersome and increases the amount of code.
You can refactor by using Readonly.
readonly a : string;
readonly b: string;
readonly c: string;
readonly d: string;
} = {
a: ‘a‘,
b: ‘b‘,
c: ‘c‘,
d: ‘d‘
}
// ↓
const obj: Readonly<{
a : string;
b: string;
c: string;
d: string;
}> = {
a: ‘a‘,
b: ‘b‘,
c: ‘c‘,
d: ‘d‘
}
Happy Coding☀️
