Question 52154 in Javascript Question posted in
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Traffic signal light in JS using array and conditions – Javascript

I am trying to build a traffic signal light.

there will be a variable called signal where green, yellow, and red are stored as a value of that variable. If the traffic light shows red light, that means there is danger. If the traffic light shows yellow light, I should stop. If there is a green light, I can cross the road.

My code is :

var signal = ["green", "yellow", "red"];

if (signal == "red") {
    console.log("Danger");
}

else if (signal == "yellow") {
    console.log("Stop");
}

else {
    console.log("Cross the road");
}

I am expecting, if I select one color, then it will show the only output as I mentioned previously

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2

Answers


  1. 0

    You Code flow is not correct for solve your problem.

    Array values are not required to check.

    You simply check with if…else Condition.

    // you can change value to get your results - "green", "yellow", "red"

var signal = "green"; 

if (signal == "red")
{console.log("Danger");
}
else if (signal == "yellow"){
console.log("Stop");
}else {
console.log("Cross the road");
}
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  2. 0

    Your variable signal has the value ["green", "yellow", "red"] and since you don’t change it ever, it can never be "red", "yellow" or "green". One is an array of strings, while the other is just a string.

    You are lacking a piece in your model, which is the current signal.

    var signals = ["green", "yellow", "red"];
var currentSignal = "red";

if (currentSignal === signals[2]) {
    console.log("Danger");
}

else if (currentSignal === signals[1]) {
    console.log("Stop");
}

else {
    console.log("Cross the road");
}

    But that’s a bit hard to read, with indexing the array and stuff. And what if currentSignal is set to "teal"? So let’s just refactor your signals into some sort of enumeration, or just a plain object:

    var signals = {
  red: "red",
  yellow: "yellow",
  green: "green"
};

var currentSignal = signals.green;

if (currentSignal === signals.red) {
    console.log("Danger");
}

else if (currentSignal === signals.yellow) {
    console.log("Stop");
}

else {
    console.log("Cross the road");
}

    In a simple scenario this would now suffice, but technically you could still assign currentSignal a value of say … "" or "black", because javascript does not handle types very well, so you could (or should) add another condition:

    var signals = {
    red: "red",
    yellow: "yellow",
    green: "green"
};

var currentSignal = "3 double whoppers";

if (currentSignal === signals.red) {
    console.log("Danger");
}

else if (currentSignal === signals.yellow) {
    console.log("Stop");
}

else if (currentSignal === signals.green) {
    console.log("Cross the road");
}
else {
    throw new Error("invalid signal detected");
}

    And of course, depending on your preferences you also use a switch statement:

    switch(currentSignal) {
    case signals.red:
    console.log("Danger");
    break;
  case signals.yellow:
    console.log("Stop");
    break;
  case signals.green:
    console.log("Cross the road");
    break;
  default:
    throw new Error("invalid signal detected");
}
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