Question

I am having trouble getting my content script request values from my background script.

content_script.js
=================
var elements = undefined
var properties = undefined
var targets = undefined
chrome.extension.sendRequest({greeting: "elements"}, function(response) {
    elements = response.input;
});
if (elements == undefined){
    var elements = ["a","img"];
}else{
    elements = elements.split(',');
}
chrome.extension.sendRequest({greeting: "properties"}, function(response) {
    properties = response.input;
});
if (properties == undefined){
    var properties = ["alt","id","class"];
}else{
    properties = properties.split(',');
}
chrome.extension.sendRequest({greeting: "targets"}, function(response) {
    targets = response.input;
});
if (targets == undefined){
    var targets = ["onclick","href"];
}else{
    targets = targets.split(',');
}...
...More code and references to elements following...

The above code only works when there is a break in the code (ie waiting) before doing any relating to the values set above, I suppose I could put something to do that but i would prefer to use a more efficient solution if possible.

(for reference:)

background.js
=============
chrome.extension.onRequest.addListener(
function(request, sender, sendResponse) {
    switch (request.greeting){
        case "elements":
                var elements = localStorage["elements"];
                sendResponse({input: elements});
                break;
        case "properties":
                var properties = localStorage["properties"];
                sendResponse({input: properties});
                break;
        case "targets":
                var targets = localStorage["targets"];
                sendResponse({input: targets});
                break;
        }
  });

I have been at this for 3 hours (still learning what I’m doing with JS)

Answer 1

Uhhhhhm you cannot do that:

chrome.extension.sendRequest({greeting: "properties"}, function(response) {
    properties = response.input;
});
if (properties == undefined){ // always undefined
    var properties = ["alt","id","class"];
}else{
    properties = properties.split(',');
}

sendRequest is async.

And the correct way of checking for undefined is:

if (typeof properties == "undefined") 

If you need all that stuff just make 1 request and do all your stuff inside the callback:

chrome.extension.sendRequest({greeting: "all"}, function(response) {
    if (response.elements === null) {
        var elements = ["a","img"];
    } else {
        var elements = response.elements.split(',');
    }

    if (response.properties === null) {
        var properties = ["alt","id","class"];
    } else {
        var properties = response.properties.split(',');
    }

    if (response.targets === null) {
        var targets = ["onclick","href"];
    } else {
        var targets = response.targets.split(',');
    }
});

And in background:

chrome.extension.onRequest.addListener(function(request, sender, sendResponse) {
    switch (request.greeting){
        case "all":
            sendResponse({
                elements: localStorage.getItem("targets"),
                properties: localStorage.getItem("properties"),
                targets: localStorage.getItem("targets")
            });
            break;
    }
});