Develop Reference

Javascript switch case keeps skipping to the default case

My Switch case keeps on going to default.
The condition is from the intersectionWord which outputs a specific keyword from an array which matches up to a word in the trigger word array aka an intersectionWord.
const TriggerWord = ["weather", "add", "multiply", "divide", "subtract", "hi", "hello",];
const intersectionWord = TriggerWord.filter(element => request.requestContent.includes(element));
And the objective was to pass that trigger word into the switch statement to evaluate if any of those cases match up. If they do match up it should output an alert. But currently it just seems to go straight to the default case every time.
I don't know where it is going wrong.
switch (intersectionWord) {
case TriggerWord[0].toString:
alert("Checking the weather");
break;
case TriggerWord[1].toString:
alert("Doing the math");
break;
case TriggerWord[2].toString:
alert("Doing multiplication");
break;
case TriggerWord[3].toString:
alert("Doing the division");
break;
case TriggerWord[4].toString:
alert("Doing the subtraction");
break;
case TriggerWord[5].toString:
alert("Just saying Hello");
break;
case TriggerWord[6].toString:
alert("Just saying Hello");
break;
default:
alert("I couldn't find a TriggerWord");
}

As noted in the comments, there are two problems with your code:
You're missing the () after .toString so it will call the function; also, it's not necessary to use .toString(), since they're already strings.
intersectionWord is an array, so it will never be equal to any of the strings in TriggerWords.
Instead of the switch/case statement, consider using an object:
const messages = {
weather: "Checking the weather",
add: "Doing the math",
multiply: "Doing multiplication",
...
}
Then you can loop over intersectionWords, looking up the corresponding message:
intersectionWords.forEach(word => alert(messages[word]))
Or you could combine them all into a single message:
let actions = intersectionWords.map(word => messages[word]).join(", ");
if (actions) {
alert(actions);
} else {
alert("No matching activity");
}

TypeError: if 'false' not working as expected

I'm doing a PWA quiz application using React.js and I've met the following problematic:
I can get questions objects with only one answer, and some with multiple.
In the case there is only one possible answer, I want to force the user to only have one possibility.
To do that, I made the following algorithm:
clickOnChoice = (key) => {
if (this.state && this.state.correctAnswers) {
let newChoices = INITIAL_CHOICES; // {}
if (this.state.multiChoice) {
console.log("this.state.multiChoice:", this.state.multiChoice); // this.state.multiChoice: false ???
newChoices = JSON.parse(JSON.stringify(this.state.choices)); // {answer_b: 1}
}
newChoices[key] = 1 - (newChoices[key] | 0); // {answer_b: 1, answer_a: 1}
this.setState({
choices: newChoices
}, this.updateNextButtonState);
}
}
However the execution seems to ignore the condition if (this.state.multiChoice).
What am I missing?
Maybe I need a cup of coffee... ☕
Anyway, thanks in advance!

It is more than likely you are trying to checking a string of 'false' rather than an actual boolean value.
you can check that the string is the expected boolean if (this.state.multiChoice === 'true') or change the value of the state property to true || false

Pattern matching in JavaScript?

I need to create a variable in JavaScript and assign it's value based on a condition. This works but feels a bit verbose:
const color = (() => {
switch (type) {
case "primary":
return CONSTANTS.colors.primary;
case "secondary":
return CONSTANTS.colors.secondary;
case "tertiary":
return CONSTANTS.colors.tertiary;
case "positive":
return CONSTANTS.colors.positive;
case "negative":
return CONSTANTS.colors.negative;
case "disabled":
return CONSTANTS.colors.disabled;
default:
throw new Error("A backgroundColor condition was missed");
}
})();
Is what I'm trying to do called "pattern matching"? Ive read that JavaScript doenst have this feature but Im not totally sure what it is.
Is there a more concise way of writing the code above? I could have lots of if statement but this feels messier and requires the variable to be let not const.
let color:
if (type === "primary") {
color = CONSTANTS.colors.primary;
} else if(type === "secondary") {
color = CONSTANTS.colors.secondary;
} else if(type === "tertiary") {
color = CONSTANTS.colors.tertiary;
} else if(type === "secondary") {
color = CONSTANTS.colors.secondary;
} else if(type === "positive") {
color = CONSTANTS.colors.positive;
} else if(type === "negative") {
color = CONSTANTS.colors.negative;
} else if(type === "disabled") {
color = CONSTANTS.colors.disabled;
}

The easiest solution for your problem is to check if the type is defined in the object CONSTANTS.colors. If you want to access a property by variable, you need to use the bracket annotation. Everything inside the brackets is evaluated as an expression (so type is a variable, 'type' the String value). Therefore, object.type returns the same value as object['type'].
let color = null;
if (typeof CONSTANTS.colors[type] !== 'undefined') {
color = CONSTANTS.colors[type];
} else {
throw new Error('A backgroundColor condition was missed');
}
console.log(color);
You can also first check if the key is defined in the object with Object.keys() and includes():
let color = null;
if (Object.keys(CONSTANTS.colors).includes(type)) {
color = CONSTANTS.colors[type];
} else {
throw new Error('A backgroundColor condition was missed');
}
console.log(color);
If you want to support IE11, you cannot use .includes(). Use .indexOf(type) !== -1 instead of .includes(type).

Pattern matching is generally referring to matching arguments passed to a function: testing to see if they match a specific "pattern". For example, a pattern match might allow you to write a function that takes an integer argument in "two different ways", one where the argument passed in is 0 and one when the argument passed is not 0 (the "otherwise" case). Switch statements are somewhat similar to this type of branching logic but aren't the same as a purely functional language like Haskell, and don't quite help with your goal here.
How about something like this instead?
const myColor = CONSTANTS["colors"][type];
if(typeof myColor !== 'undefined') {
color = myColor;
} else {
throw new Error("A backgroundColor condition was missed");
}

You are looking for property accessor:
color = CONSTANTS.colors[type];

An easy replacement for your code would be
const color = (() => {
const color = CONSTANTS.colors[type];
if (!color) {
throw new Error("A backgroundColor condition was missed");
}
return color;
}
})();
And no, that is not pattern matching.

I think it is wise to introduce an Enum that will hold the color values.
var ColorType = {
Primary: "primary",
Secondary: "secondary",
Tertiary: "tertiary,
...
};
Then you can use this enum in switch case and you will avoid the typos and referrence to string directly.
I think it will make the code less verbose and less prone to errors.

You can access a property of an object by using the property name as a string in square brackets.
(This example doesn't include the error catching you were using in your switch statement, but you can add that.)
const CONSTANTS = {
colors: {
primary: "blue",
secondary: "yellow"
}
}
function getColor(myPropName){
// Pass dynamic property names like this
return CONSTANTS.colors[myPropName];
}
console.log(getColor("secondary"));

Switch statement not working within JSX (React.js)

I am trying to make my switch work within JSX, but for some reason it doesn't work.
Every output has an ID, which is I. Now I am trying to make a switch statement with I, but it will always return the default value.
Why?
My code:
{(() => {
switch (i) {
case "0": return "{indents}";
case "1": return "{indents2}";
case "2": return "{indents3}";
default: return "{indents3}";
}
})()}
This is all within a div with attribute key={i}.

I would recommend maps instead. Maps/objects are type insensitive. It will also reduce execution complexity:
const map = {
0: indents,
1: indents2,
2: indents3
}
<div>{map[i] || indents3}</div>
Alternatively, since you are using 0,1,2.., you can also have it as an array.
const map = [indents, indents2, indents3];
<div>{map[i] || indents3}</div>

How to simplify multiple if statements javascript?

I have multiple conditions to check. I have to add icons based on the conditions, Then I need to change the background color based on some other set of conditions. I am using if statement. This is my code.
JSON:
{
"date": "2017-05-12",
"a": false,
"b": true,
"c": true,
"d": false,
"status": "active"
}
Javascript:
if (date != -1) {
//do something
if (a) {
//Add icon a
}
if (b) {
//Add icon b
}
if (c) {
//Add icon c
}
if (d) {
//Add icon d
}
}
if(status == "active"){
//Background Green
}
else if (status == "onhold"){
//Background Yellow
}
else if (status == "inactive"){
//Background Red
}
else{
//Backgeound Grey
}
How do I simplify it?

The first half of you code looks fine.
For the second half of your code you should make use of a switch statement. These replace the if-else statements you are using and decide what to do when certain "cases" occur. For example:
switch(status) {
case 'active':
//background green
break;
case 'onhold':
//background yellow
break;
case 'inactive':
//background red
break;
default:
//background grey
break;
}

My idea is：
var icons = {
a: 'a.png',
b: 'b.png',
c: 'c.png',
d: 'd.png',
}
if (date != -1) {
Object.keys(icons).forEach(function(key) {
if (data[key]) {
//Add icon icons[key]
}
});
}
var statusColors = {
active: 'Green',
onhold: 'Yellow',
inactive: 'Grey',
}
//Background statusColors[status]

I think it is pretty good as it is. Is is better to have understandable code than complex code that does exactly the same thing.
You don't have to do
if (a === true)
as it's equivalent to
if ( a )

There is no way to "simplify" it, but you can try to use switch statement instead:
switch (status) {
case 'active':
// active
break;
case 'onhold':
// onhold
break;
case 'inactive':
// inactive
break;
default:
console.log('default');
}
You can even "group" some conditions:
switch (status) {
case 'active':
case 'onhold':
// active AND onhold case
break;
case 'inactive':
// inactive
break;
default:
console.log('default');
}
More about switch statement -> https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Statements/switch

For Status variable you can use switch but for the first condition you have to use if-else statements I think.
switch (status) {
case "active":
//Background Green
break;
case "onhold":
//Background Yellow
break;
case "inactive":
//Background Red
break;
default:
//Backgeound Grey
}

a?setIconA():b?setIconB:c?setIconC;d?setIconD
and
status == "active" ? setGreen() : status == "onhold": setYellow()
and so on.

Your question doesn't quite give the details of the actions in each case, but if they're very similar, and there's a match between the property name and whatever action you need to take, you can use loops.
['a','b','c','d'].forEach(function (k)
{
if (objectFromJSON[k])
{
addIcon(k);
}
});
For the second part, it's slightly more complex as you have status names that don't match the color. You can either:
define CSS classes with those status names, and use the status name to set the class:
CSS:
.status-active
{
background: green;
}
.status-onhold
{
background: yellow;
}
.status-inactive
{
background: red;
}
JS:
theHTMLobject.classList.addClass('status-'+objectFromJSON.status);
use an object's properties (or a Map) to convert the status into a color

Do you mean "simplify" or do you mean "shorten" - because the two are almost mutually exclusive (shorter code is often not simpler!)
Your code is clear, and understandable. But it is a bit verbose, and can get much more complex as things grow. Sometimes it is better to shorten and the risk of making it a bit harder to understand.
You could consider things like a map between the status and the appropriate color
var backgroundStatusMap = {
"active":"green",
"onhold": "yellow",
"inactive": "red"
};
var backgroundColor = backgroundStatusMap[json.status];
Things like this can be added to easier if you as add new statuses - without having to trawl for the right place to put a new if.. condition.
Similarly, you could create a map for the booleans-to-icons
var iconMap = {
"a":"icon_a.png",
"b": "icon_b.png"
};
function getIcon(json, prop){
if(json[prop])
return iconMap[prop];
return null;
}
var iconA = getIcon(json,"a");
var iconB = getIcon(json,"b");