In this action I am trying to say...
if VS_WRNG is Blank and if VS_WRNG is DSC or DSQ then set the two items
but when I click on VS_WRNG in my web app and select DSC it didn't autofill the BOB_TYPE answer with LIN.
Did I screw up the code or is it the ! not working like that and do I need to do a switch (true) & case (VS_WRNG != "")?
//Set BoB Type [TEMPORARY]
switch (!VS_WRNG) {
case "":
switch (VS_WRNG) {
case "DSC":
case "DSQ":
switch (VS_BTYP) {
case "":
setValue('BOB_TYPE',"LIN");
VS_BTYP = "LIN";
break;
}
break;
}
break;
}
Thanks
The primary issue you're having is that !VS_WRNG always results in a boolean. It can never result in an empty string "". So the case "": will never run. But even if it did, your code still won't work:
In this action I am trying to say... if VS_WRNG is Blank and if VS_WRNG is DSC or DSQ then set the two items
VS_WRNG cannot be simultaneously Blank and DSC or DSQ. You need to rethink your logic - the requirements are incompatible right now and quite illogical.
This is also quite an abuse of switch statements. If your switch statement has one case, it's an if statement. Just use an if statement like this:
if(VS_WRNG === "") { ... }
Your middle switch statement can be implemented also with an if statement, since you've written it to just check for two conditions:
if(VS_WRNG == "DSC" || VS_WRNG == "DSQ") { ... }
Related
I'm wondering if it would be better to use a switch statement in my specific case.
I'm writing an Alexa Custom Skill, and I need to "redirect" to the appropriate intent depending on the available information (aka slots). Below is what I have currently (using if/else):
if (_type === "IntentRequest") {
this.handler.state = states.START;
if (_slots.indexOf("address") != -1) {
this.emitWithState("GoingToAddressIntent");
} else if (_slots.indexOf("place") != -1) {
this.emitWithState("GoingToPlaceIntent");
} else if (_slots.indexOf("type") != -1) {
this.emitWithState("GoingToTypeIntent");
} else if (_slots.indexOf("purpose") != -1) {
this.emitWithState("GoingToPurposeIntent");
} else {
this.emit("Unhandled");
}
}
I expect _slots to be an array of any permutations of the four elements, [ "address", "place", "type", "purpose" ]. Therefore, it could be anything from [ "address" ] to [ "place", "purpose" ] to etc. etc., but always in the same order (e.g. [ "purpose", "address" ] would never happen).
The order of the comparisons matters because there is a "hierarchy" of information; so if the "address" slot is present, I have to emit the "GoingToAddressIntent" regardless of what other slots are available. Given this requirement, I thought using a switch statement maybe more straightforward and readable despite having to have a few extra lines of code to "convert" the array of strings to an array of booleans. It clearly lays out the hierarchy & make sure they are evaluated in order. I could do:
if (_type === "IntentRequest") {
this.handler.state = states.START;
slots = [
_slots.indexOf("address") != -1,
_slots.indexOf("place") != -1,
_slots.indexOf("type") != -1,
_slots.indexOf("purpose") != -1
]
switch(slots.indexOf(true)) {
case 0:
this.emitWithState("GoingToAddressIntent");
break;
case 1:
this.emitWithState("GoingToAddressIntent");
break;
case 2:
this.emitWithState("GoingToTypeIntent");
break;
case 3:
this.emitWithState("GoingToPurposeIntent");
break;
default:
this.emit("Unhandled");
}
}
... in which case I have an extra line to define the array of booleans, use indexOf() to get the index of the first occurrence of a true literal (because all 4 slots are always in the order of hierarchy), and run it through the switch statement. However I wanted ask experts on their ideas of what best programming practice is in this case and the reasoning behind it because I want this to become a long-term project that is maintainable, and also I believe I can learn something from their insights.
Please leave a comment if you think this should be migrated to another community on SE, but from my research (although 3 years old) I believe this should be fine (I'm just not 100% confident on this).
If they're always in the order of precedence in _slots, maybe you could make a hash map to the state you're going to emit...
const map = {
address: "GoingToAddressIntent",
place: "GoingToPlaceIntent",
type: "GoingToTypeIntent",
purpose: "GoingToPurposeIntent"
};
const state = map[_slots[0]];
if (state) {
this.emitWithState(state);
} else {
this.emit("Unhandled");
}
I wouldn't go with your example of the switch statement. People could understand what you're attempting to do, but it does seem pretty convoluted. I use switch statements pretty liberally, mostly in backend code, and I think it could work fine here. A group of if/else is fine too, since there's only 4 cases you need to work through. Lets roll with the switch statement since that's what you're asking about.
Based on your explanation, the order is always going to be the same, although the first value you get may be different. So the solution would be to simply grab the first value, and switch over that.
if (!!slots.length) {
var keyword = slots[0];
switch (keyword) {
case 'address':
this.emitWithState("GoingToAddressIntent");
break;
case 'place':
this.emitWithState("GoingToPlaceIntent");
break;
case 'type':
this.emitWithState("GoingToTypeIntent");
break;
case 'purpose':
this.emitWithState("GoingToPurposeIntent");
break;
default:
this.emit('Unhandled'); // I typically throw an exception here
}
}
Okay, so this may be a repeat, but I personally haven't seen anything on the internet or in Stackoverflow about this.
I am working on a game project and I have been trying to make a text-based game.
In this game, I have a switch statement, for when the user enters a command.
So far I have things for Inventory and Look (Look around the environment), but how do I work with specific things in a switch statement?
For example:
submit = function(input) {
switch(input) {
case "LOOK":
lookaround();
break;
case "LOOK AT" + item:
look();
}
}
It is the LOOK AT line I am having issues with. I do not know how I can make a string work in that format, unless I had a case for every single item individually, example case "LOOK AT ORANGE" or case "LOOK AT TREE".
I hope I am explaining this thoroughly enough. Can anyone give me some advice?
Thanks
EDIT
I think it is important to note that the user is typing the input into an input box, so the value of the input is going to be a string.
If it will help to see the code I have made, please let me know in the comments below.
EDIT
THANKS FOR YOU HELP GUYS!
I used a regular expression (Thanks #red-devil) and a mixture of slicing. It works perfectly now!
Switch works with constants, not expressions like 'LOOK AT' + anything.
You could define an object for map any of your cases to your own functions. Like that:
var looks = {
'lookat-something' : function() {
alert('something');
},
'lookat-other-thing' : function() {
alert('other thing');
},
};
var x = 'lookat-other-thing';
looks[x]();
It much more flexible than using switch in any way.
If I understood you right, you want the user to be able to input LOOK AT and then any item name. The problem here is that you have this ominous item variable that could stand for anything and this is not going to work.
I would suggest one of these two ways:
Going along the lines of your example:
submit = function (input) {
switch (true) {
case input == "LOOK":
alert("Look")
break;
case input.startsWith("LOOK AT"):
alert(input)
break;
}
}
if (typeof String.prototype.startsWith != 'function') {
String.prototype.startsWith = function (str) {
return this.slice(0, str.length) == str;
};
}
And secondly, and this is the method I would recommend, you implement a way to parse any input into a command and parameters. A way to do this is to split the input at every space character and then the first value is the command and the rest would be the parameters. This would require you to use a one word command like LookAt and not LOOK AT.
So something like this:
function submit(input) {
var parts = input.split(" ");
var cmd = parts[0];
var args = parts.slice(1);
switch (cmd) {
case "Look":
lookAround();
break;
case "LookAt":
lookAt(args[0]);
break;
}
}
My question divide in three questions:
1.Is it even possible ?
2.If yes can we do it with the default value ?
3.Or could with do it outside the switch statement ?
Example for questions 2:
switch(stuff) {
case 'something':
some event;
break;
case 'the case that could be add by the default element':
some event that could happen only after the code was executed
default:
magic code that would add another case element
}
Example for question 3:
switch(stuff) {
case 'something':
some event;
break;
case 'the case that could be add by the magic code':
some event that could happen only after the code was executed
default:
some default event
}
magic code that would be executed after the switch and that would add a case
You can't really code JavaScript so that it will modify itself, but you can code a switch statement such that certain cases will be ignored initially and then "turned on" later:
var enableCase = false;
switch(true) {
case stuff === 'something':
// some code;
break;
case enableCase && stuff === 'the case not initially enabled':
// some code
break;
default:
// turn on previous case:
enableCase = true;
break;
}
Having said that, I don't really recommend doing it. There is almost certainly a more sensible way to implement this depending on the underlying problem you are trying to solve. Perhaps with an if/if else/else block that tests a flag set elsewhere.
First time writing Javascript. I just would like know if there is a shorter way of writing this:
<p id="demo"></p>
<script>
function myFunction() {
var letter = document.getElementById("myInput").value;
var text;
if (letter === "5544") {
text = "Abar, Marlon 1,800";
} else if (letter === "5545") {
text = "Pia, Darla 1,800";
} else if (letter === "5546") {
text = "Salazar, Alex 1,500";
//etc...
} else {
text = "Incorrect Account Number";
}
document.getElementById("demo").innerHTML = text;
}
</script>
Tried map but I couldn't get it to work.
There isn't really a shorter way to write an if statement in that way (which I will assume is what you're asking). However, there could be a few different ways to write this depending on how many things you want to check.
Use a Switch statement
There is a cleaner way when dealing with multiple cases that letter could be.
This would be a switch statement and it would look like this:
var text;
switch (letter) {
case "5544":
text = "Abar, Marlon 1,800";
break;
case "5545":
text = "Pia, Darla 1,800";
break;
// more cases
default:
text = "Incorrect Account Number";
break;
}
This reads a little better than an if else statement in some cases. The default keyword here acts as your else clause in an if else statement. The case acts as your different if statements if you will.
Essentially, the switch statement above will fall through each of the cases it defines until it finds a case that matches letter (such as "5544"). If none matches, it hits the default case. The break keyword at the end of each case stops things from falling through to the next defined case once a match is found.
This method could get cumbersome with more than 6 or 7 cases.
Create an object and look up the value
Now, a shorter way to get the value you want could be to define an object and get the value based on what has been entered like so:
var letter = document.getElementById('selector').value;
var obj = {
'5544': 'Abar, Marlon 1,800'
};
if (letter in obj) {
// do something if found
}
else {
// do something if not found
}
This could be an easy way to get a value if you have many values to check.
Other thoughts
As a side note to all of this, there are short hand if statements called ternary statements which you can find here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator ... However, I would not recommend nesting these as it becomes very complicated and not very readable.
Conclusion
So, to reiterate the answer to your question: No, there isn't really a shorter way to write an if else statement with many values. You can use a switch statement to make it cleaner. Use the object lookup method if you have many values you would like to check.
JavaScript has object (map) literals. Use them for terse code. In your final application you'll get the data for the map from someplace else and not code it directly into your website, but if you did, it would look like this:
document.getElementById( "demo" ).innerHTML = {
"5544" : "Abar, Marlon 1,800",
"5445" : "Pia, Darla 1,800",
...
}[ document.getElementById( "myInput" ).value ];
you can use switch for a long if - else -if ladder:
switch(expression) {
case n:
code block
break;
case n:
code block
break;
default:
default code block
}
This is how it works:
1)The switch expression is evaluated once.
2)The value of the expression is compared with the values of each case.
3)If there is a match, the associated block of code is executed.
if you need basic tutorials in java script then you should try w3 schools.
Here is a snippet of JavaScript code from a tutorial I was working with. I don’t understand why it doesn’t end with a final else clause; I thought that was a rule.
var curScene = 0;
function changeScene(decision) {
var message = "";
if(curScene == 1) {
message = " welcome";
} else if (curScene == 2) {
message = " this is scene two";
} else if (curScene == 3) {
message = " this is scene three";
}
document.getElementById("sceneimg").src = "scene" + curScene + ".png";
if(message != ""){
alert(message);
}
}
I thought it was always supposed to end with an "else"?
The else block is optional. You can have if without else.
For the same reason as why you can have just a single if:
if( /*condition*/ ) {
//some code
}
//other stuff
Consider 3 Scenario
Scenario 1: Boolean condition
if (condition) {}
else {}
Specifying a condition as else if would be redundant, and it's really obvious to the reader what the code does. There is no argument for using else if in this case.
Scenario 2: Infinite states
Here we are interested in testing for conditions A and B (and so on), and we may or may not be interested in what happens if none of them holds:
if (conditionA) {}
else if (conditionB) {}
else {} // this might be missing as it is in your case
The important point here is that there isn't a finite number of mutually-exclusive states, for example: conditionA might be num % 2 == 0 and conditionB might be num % 3 == 0.
I think it's natural and desirable to use a reasonable amount of branches here; if the branches become too many this might be an indication that some judicious use of OO design would result in great maintainability improvements.
Scenario 3: Finite states
This is the middle ground between the first two cases: the number of states is finite but more than two. Testing for the values of an enum-like type is the archetypal example:
if (var == CONSTANT_FOO) {}
else if (var == CONSTANT_BAR) {} // either this,
else {} // or this might be missing
In such cases using a switch is probably better because it immediately communicates to the reader that the number of states is finite and gives a strong hint as to where a list of all possible states might be found (in this example, constants starting with CONSTANT_). My personal criteria is the number of states I 'm testing against: if it's only one (no else if) I 'll use an if; otherwise, a switch. In any case, I won't write an else if in this scenario.
Adding else as an empty catch-errors block
This is directly related to scenario #2 above. Unless the possible states are finite and known at compile time, you can't say that "in any other case" means that an error occurred. Seeing as in scenario #2 a switch would feel more natural, I feel that using else this way has a bad code smell.
Use a switch with a default branch instead. It will communicate your intent much more clearly:
switch(direction) {
case 'up': break;
case 'down': break;
default: // put error handling here if you want
}
This might be a bit more verbose, but it's clear to the reader how the code is expected to function. In my opinion, an empty else block would look unnatural and puzzling here.
It doesn't have to, for the same reason an if on its own doesn't require an else.
Usually it's a good idea to have one, as a sort of "catch-all" situation, but the above code could be written as:
switch(curScene) {
case 1: message = " welcome"; break;
case 2: message = " this is scene two"; break;
case 3: message = " this is scene three"; break;
}
In the above code, I could also add:
default: message = " invalid curScene value"; break;
But it's completely optional to do so. It depends on how reliable the curScene variable is whether or not I personally would add it in.
Not having an else clause is fine syntactically. MDN Documentation Basically the second if becomes the body of the else, see the section on "how it would look like if the nesting were properly indented".
As to whether it's bad practice I think that depends on intent. By not explicitly defining the final else clause, you might end up with a bug where a condition you didn't cover comes through. Consider this:
if(myVariable > 0) {
doSomething();
} else if(myVariable < 0) {
doSomethingElse();
}
Nothing happens if myVariable is 0. It would be hard to see if you were just glancing through the code. I would say if you run into this pattern it would be a code smell, something might be wrong, but it could be fine.
The same logic could always be expressed with nested if statements. I would go with whatever is more readable.
else is a default case for the if statement.
If there is no else then if none of the conditions in the if or else if cases are met than the if statment will do nothing.
Usually it is good practice to have a default case but there are a lot of times where it is not necessary and thus excluded from the code.
In this case, if the curScene was anything other than 1, 2, 3 then the else statment would be used, but since there is no processing to be done on other cases the coder has not included an else.
yes, always have a else is VERY GOOD habit(when using with if-elseif). sometimes people might even write this:
if(curScene == 1) {
message =" welcome";
else if (curScene == 2) {
message = " this is scene two";
}
else if (curScene == 3) {
message = " this is scene three";
} else {
// empty.
}
to tell people there is indeed nothing to do in the else.
change the if condition for answer validation if(answer==100) to if(answer===100)
it is working fine now...