How can I access variables outside of current scop

问题:

I'm writing an application in javascript and cannot figure it out how to access the variables declared in my function, inside this jquery parse. Inside I can access global variables, but I don't really want to create global vars for these values.

Basically I want to extract file names from an xml document in the simulationFiles variable. I check if the node attribute is equal with the simName and extract the two strings inside the xml elements, that part I think it's working.

How can I extract those xml elements and append them to local variables?

function CsvReader(simName) {
    this.initFileName = "somepath";
    this.eventsFileName = "somepath";
    $(simulationFiles).find('simulation').each(function() {
       if ($(this).attr("name") == simName) {
           initFileName += $(this).find("init").text();
           eventsFileName += $(this).find("events").text();
       }
    });
}   

回答1:

The this in the CsvReader function is not the same this in the each() callback (where instead it is the current element in the iteration). To access the scope of the outer function within the callback, we need to be able to reference it by another name, which you can define in the outer scope:

function CsvReader(simName) {
    this.initFileName = "somepath";
    this.eventsFileName = "somepath";
    var self = this; // reference to this in current scope
    $(simulationFiles).find('simulation').each(function() {
       if ($(this).attr("name") == simName) {
           // access the variables using self instead of this
           self.initFileName += $(this).find("init").text();
           self.eventsFileName += $(this).find("events").text();
       }
    });
}

回答2:

I made a working demo (I changed it to use classes so it would work with HTML).

function CsvReader(simName) {
    this.initFileName = "somepath";
    this.eventsFileName = "somepath";
    var context = this;
    $(simulationFiles).find('simulation').each(function() {
       if ($(this).attr("name") == simName) {
           context.initFileName += $(this).find("init").text();
           context.eventsFileName += $(this).find("events").text();
       }
    });
}   

回答3:

The simplest change you can do to make it work is... Change your function in each from normal ( function() {}) to arrow function ( () => {} ) that will automatically take the context of the function in which it is defined.