Error: Initializer of instance member variable 'x' cannot reference identifier 'y' declared in the constructor. #2548

mpawelski · 2015-03-30T14:03:24Z

I got this error:

Initializer of instance member variable 'objectWithFunc' cannot reference identifier 'param' declared in the constructor.

for this piece of code:

interface ITest {
    foo: string;
    bar: string;
}

var param: ITest = null;

class Test {    

    constructor(param: ITest) {        
    }

    method() {        
        console.log(param.foo);
    }

    private objectWithFunc = {
        func: () => {
            console.log(param.foo);            
        }
    }
}

When I change parameter name in constructor to other name (for example constructor(param2: ITest)) it compiles.

This behaviour was surprising for me. Is it a bug?

The text was updated successfully, but these errors were encountered:

mpawelski · 2015-03-30T14:04:28Z

I'm using Typescript 1.4 with Visual Studio Community 2013.

mhegazy · 2015-03-30T18:11:41Z

This is by design. Property initialization happens as part of constructying the object. the compiler will generate it as part of the constructor, that means that your constructor parameter "param" will shadow the variable "param" at runtime. this error message is letting you know that this is going to happen.

so the following ts code:

var param = null;
class Test {    
    constructor(param) {        
       //constructor body 
    }
    private property = param; // initialization
}

will be transformed to:

var param = null;
var Test = (function () {
    function Test(param) {
        this.property = param; // initialization
        //constructor body 
    }
    return Test;
})();

mhegazy added the By Design label Mar 30, 2015

RyanCavanaugh closed this as completed Mar 30, 2015

microsoft locked and limited conversation to collaborators Jun 18, 2018

Error: Initializer of instance member variable 'x' cannot reference identifier 'y' declared in the constructor. #2548

Error: Initializer of instance member variable 'x' cannot reference identifier 'y' declared in the constructor. #2548

mpawelski commented Mar 30, 2015

mpawelski commented Mar 30, 2015

mhegazy commented Mar 30, 2015

Error: Initializer of instance member variable 'x' cannot reference identifier 'y' declared in the constructor. #2548

Error: Initializer of instance member variable 'x' cannot reference identifier 'y' declared in the constructor. #2548

Comments

mpawelski commented Mar 30, 2015

mpawelski commented Mar 30, 2015

mhegazy commented Mar 30, 2015