Is it possible to return the result of javascript method while executing that in shell script?

Question

I am new to javascript. I have a js file something like below(test.js):

async function getData() {
   let a =100;
   // Some other function calls which modifies a
   // Some more console logs here.
   return a;
}
(async () => {
  console.log(await getData()); // When trying to return await getData() giving some error.
})();

I am executing the above script output = $(node test.js) in shell script and I need the value of a in the shell script but here I am getting all the console.log statements. Is it possible to get the value?

I tried that, but it also printing all console log statements along with the returned value. — lakshmiravali rimmalapudi
– lakshmiravali rimmalapudi, Commented Aug 22, 2021 at 8:44
is it because of the spaces? shell is very picky about spaces, pls make sure it's output=$(node test.js) and there is no space around the = sign — tsamridh86
– tsamridh86, Commented Aug 22, 2021 at 8:58
Have a look at process.stdout. With stdout you print out stuff so that it can be used by other application. Maybe this can also help: bash - How to handle stdout in node.js - Stack Overflow — chrwahl
– chrwahl, Commented Aug 22, 2021 at 9:08

Hackrrr · Accepted Answer · 2021-08-22 11:32:22Z

0

If you know that output will always have one line (by output I mean returned value from getData()), you can use $(node test.js | tail -n 1) to grab only one last line from node test.js. Otherwise you can do this little hacky workaround by replacing console.log function:

async function getData() {
   let a = 100;
   console.log("Some cosole log");
   console.log("Some other log");
   return a;
}
(async () => {
        console_log = console.log; // Save original function for later
        console.log = ()=>{}; // Replace original with "dummy" function
        console_log(await getData()); // Use saved original to log only what we want
})();

This will work unless some part of code use process.stdout.write to log/print data directly. To avoid this, we can again replace process.stdout.write with some dummy function but since this is likely to break some other things, I would avoid it.

answered Aug 22, 2021 at 11:32

Hackrrr

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4 Comments

lakshmiravali rimmalapudi Over a year ago

Thanks for the response. I can use one of them. I am more inclined to $(node test.js | tail -n 1)

lakshmiravali rimmalapudi Over a year ago

How to get the data if the variable returned in multi-line string variable?

lakshmiravali rimmalapudi Over a year ago

If I try to use console_log = console.log; it's saying void function return value is used.

Hackrrr Over a year ago

I assume it's just a warning from the IDE so it will be fine at runtime (as in JS you are allowed to use "void values" (functions without a return statement) as assignments). If this message bother you (like it would bother me), you can probably find some way to suppress this warning/error.

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