Switch case jumps to wrong case in javascript (how to properly use the break command)
Question
My code is not so long so I am pasting all of it here.
The code is not complete but when I run it it first jumps to case "start" which it is supposed to, and then jumps to case "end". I can see it because it prints both blocks' console log texts. Why is it jumping to the "end" case?
<html>
<body>
<script>
function stepStream(stream,step){
switch (stream[step]){
case "start":
console.log("Started reading stream...");
case "end":
var success = "Finished reading dataStream.";
console.log(success);
return success;
default:
throw "Data stream format is bad";
case "gesture":
console.log("Running case gesture! But why?");
step+=1;
stepStream(stream,step);
case "say":
step+=1;
stepStream(stream,step);
case "sleep":
step+=1;
stepStream(stream,step);
}
}
var sentence1 = "Where are my bananas? I thought you put them in my bag?";
var sentence2 = "This is a rather irritating situattion.";
var dataStream = ["start","gesture","banzai","sleep",1.0,"say",sentence1,
"say",sentence2,"gesture","kubikasige","end"];
stepStream(dataStream,0);//Second parameter sets where to start reading the dataStream.
</script>
</body>
</html>
4 answers
solution1
2 ACCPTED 2018-02-18 22:00:57
The problem is that you are missing the break keyword after your case code. Without the break, subsequent blocks will be executed, that is why end is executed after start code. You can read more about this on this W3Schools link .
Additionally, from the JS reference :
The optional break statement associated with each case label ensures that the program breaks out of switch once the matched statement is executed and continues execution at the statement following switch. If break is omitted, the program continues execution at the next statement in the switch statement.
So your code should look like:
function stepStream(stream,step){
switch (stream[step]){
case "start":
console.log("Started reading stream...");
break;
case "end":
var success = "Finished reading dataStream.";
console.log(success);
return success;
default:
throw "Data stream format is bad";
case "gesture":
//commUGesture(stream[i+1]);
//createLogLine("robot:CommU","event:gesture:"+stream[i+1]);
console.log("Running case gesture! But why?");
step+=1;
stepStream(stream,step);
break;
case "say":
step+=1;
stepStream(stream,step);
break;
case "sleep":
step+=1;
stepStream(stream,step);
break;
}
Your "end" case has a return at the end, hence the code doesn't fall through to the other cases. Ideally, there should be a break at the end of each.
solution2
0 2018-02-18 22:01:59
您忘记在开始块中添加一个break语句，因此它一直延伸到结束块。
solution3
0 2018-02-18 22:06:11
Problem is simple all switch case have to end with break or return statements in your case that is missing.
switch(var1)
{
case "start":
console.log("Started");
break;
case "end":
console.log("stopped");
return "";
.
.
.
}
solution4
0 2018-02-18 22:09:38
该代码将在第一个匹配的“ case”开始运行，但是只有在到达“ break”或“ return”语句时才停止运行。
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