Node.js Spawn vs. Execute

• child process created by spawn()

  • does not spawn a shell
  • streams the data returned by the child process (data flow is constant)
  • has no data transfer size limit

• child process created by exec()

  • does spawn a shell in which the passed command is executed
  • buffers the data (waits till the process closes and transfers the data in on chunk)
  • maximum data transfer up to Node.js v.12.x was 200kb (by default), but since Node.js v.12x was increased to 1MB (by default)

-main.js (file)

var {spawn, exec} = require('child_process');

    // 'node' is an executable command (can be executed without a shell) 
    // uses streams to transfer data (spawn.stout)  
var spawn = spawn('node', ['module.js']);     
spawn.stdout.on('data', function(msg){         
    console.log(msg.toString())
});

    // the 'node module.js' runs in the spawned shell 
    // transfered data is handled in the callback function 
var exec = exec('node module.js', function(err, stdout, stderr){
    console.log(stdout);
});

-module.js (basically returns a message every second for 5 seconds than exits)

var interval;
interval = setInterval(function(){
    console.log( 'module data' );
    if(interval._idleStart > 5000) clearInterval(interval);
}, 1000);

• the spawn() child process returns the message module data every 1 second for 5 seconds, because the data is 'streamed'
• the exec() child process returns one message only module data module data module data module data module data after 5 seconds (when the process is closed) this is because the data is 'buffered'

NOTE that neither the spawn() nor the exec() child processes are designed for running node modules, this demo is just for showing the difference, (if you want to run node modules as child processes use the fork() method instead)

The main difference is the spawn is more suitable for long-running process with huge output. spawn streams input/output with child process. exec buffered output in a small (by default 200K) buffer. Also as I know exec first spawn subshell, then try to execute your process. To cut long story short use spawn in case you need a lot of data streamed from child process and exec if you need such features as shell pipes, redirects or even you need exec more than one program in one time.

Some useful links - DZone Hacksparrow