Typescript: Namespace merged rules

 

1. Namespaces can be merged

namespace Todo {
    export let id = 2342
}

namespace Todo {
    export let title = 'todo list';
}

console.log(Todo.id, Todo.title);
// Todo.id, Todo.title can be visited.

Can not set the same name of the property.

namespace Todo {
    export let id = 2342; // Error: Cannot redeclare block-scoped variable 'id'.ts(2451)
}

namespace Todo {
    export let title = 'todo list';
    export let id = 456;  // Error: Cannot redeclare block-scoped variable 'id'.ts(2451)
}

2. Merged with interface and Class

interface Todo {
    content: string
}

class Todo {
    comment() {

    }
}

namespace Todo {
    export let title = 'todo list';
}

const todo: Todo = {
    content: 'todo content',
    comment() {
        
    }
}

The properties in Namespace is the Static properties.

class Todo {
    comment() {

    }
    static title = 'meeting' // error: Duplicate identifier 'title'.ts(2300)
}

namespace Todo {
    export let title = 'todo list'; // error: Duplicate identifier 'title'.ts(2300)
}

Can not be located prior to a Class or Function

namespace Todo { // error: A namespace declaration cannot be located prior to a class or function with which it is merged.ts(2434)
    export let title = 'todo list';
}

class Todo {
    comment() {

    }
}