使用函数参数来访问JSON Array javascript

Question

I have a basic function taking an argument. I will use this argument to as index to access the array in JSON file. I want to take advantage of this argument instead of hard-coded inside the function. However, for some reasons, javascript is not return me the right value.

var obj = {
    "first":[
        ["aaaaa"],
        ["bbbbb"],
        ["ccccc"],
        ["ddddd"],
        ["eeeee"]                   
    ]
}

I have a javascript function to access the file.

function addElement(ID) {
    console.log(obj.ID);
}

and now if I use

addElement("first"); //this return me undefined. 

I do not want to explicitly mention obj.first in order to access the right JSON object. I would like to make it more generic so that the method can be re-used. Am I missing anything here?

Thanks...

Answer 1

JavaScript supports both dot notation and a property name literal ( obj.foo ), and brackets notation and a property name string ( obj["foo"] ).* In the latter case, the string can be the result of any expression.

So you'd need brackets notation, not dot notation:

function addElement(ID) {
    console.log(obj[ID]);
}

obj.ID accesses the property ID . obj[ID] accesses the property whose name is the string from the variable ID .

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* Just for completeness: In ES6, it will support property name Symbol s in brackets notation as well, but that's not relevant to your code.