What does assignment in while condition check?





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while(a = foo())

{

    bar();

}


Is this checking:




  • If assignment is successful, run bar, or

  • If a is defined and non-null, run bar, or

  • Something else ?






javascript while-loop







share|improve this question































    3















    while(a = foo())
    
{
    
    bar();
    
}


    Is this checking:




    • If assignment is successful, run bar, or

    • If a is defined and non-null, run bar, or

    • Something else ?






    javascript while-loop







    share|improve this question



























      3












      3








      3








      while(a = foo())
      
{
      
    bar();
      
}


      Is this checking:




      • If assignment is successful, run bar, or

      • If a is defined and non-null, run bar, or

      • Something else ?






      javascript while-loop







      share|improve this question
















      while(a = foo())
      
{
      
    bar();
      
}


      Is this checking:




      • If assignment is successful, run bar, or

      • If a is defined and non-null, run bar, or

      • Something else ?






      javascript while-loop




      javascript while-loop






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Jan 3 at 2:01









      jhpratt

      3,194102433




      3,194102433










      asked Jan 3 at 1:51









      Robert C. HollandRobert C. Holland

      545324




      545324
























          1 Answer
          1






          active

          oldest

          votes


















          3














          On every iteration, it assigns the result of the foo() call to a, and if that result was truthy, it runs the loop and tries again until the result of the call is falsey.



          For example, while assigning inside a condition is generally a code smell, it's seen often enough when trying to iterate over capture groups in a global regular expression:






          const str = 'abcdefg';
          
const pattern = /(.)./g;
          
let match;
          
while (match = pattern.exec(str)) {
          
  console.log('first captured group was ' + match[1]);
          
}
          
// after the last iteration, `match` is null, so the loop stops





          If the assignment is not successful, and the cause of that non-success would throw an error, then the whole script stops due to the error. (unless there's a try / catch block around it)






          share|improve this answer


























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            1 Answer
            1






            active

            oldest

            votes








            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            3














            On every iteration, it assigns the result of the foo() call to a, and if that result was truthy, it runs the loop and tries again until the result of the call is falsey.



            For example, while assigning inside a condition is generally a code smell, it's seen often enough when trying to iterate over capture groups in a global regular expression:






            const str = 'abcdefg';
            
const pattern = /(.)./g;
            
let match;
            
while (match = pattern.exec(str)) {
            
  console.log('first captured group was ' + match[1]);
            
}
            
// after the last iteration, `match` is null, so the loop stops





            If the assignment is not successful, and the cause of that non-success would throw an error, then the whole script stops due to the error. (unless there's a try / catch block around it)






            share|improve this answer






























              3














              On every iteration, it assigns the result of the foo() call to a, and if that result was truthy, it runs the loop and tries again until the result of the call is falsey.



              For example, while assigning inside a condition is generally a code smell, it's seen often enough when trying to iterate over capture groups in a global regular expression:






              const str = 'abcdefg';
              
const pattern = /(.)./g;
              
let match;
              
while (match = pattern.exec(str)) {
              
  console.log('first captured group was ' + match[1]);
              
}
              
// after the last iteration, `match` is null, so the loop stops





              If the assignment is not successful, and the cause of that non-success would throw an error, then the whole script stops due to the error. (unless there's a try / catch block around it)






              share|improve this answer




























                3












                3








                3







                On every iteration, it assigns the result of the foo() call to a, and if that result was truthy, it runs the loop and tries again until the result of the call is falsey.



                For example, while assigning inside a condition is generally a code smell, it's seen often enough when trying to iterate over capture groups in a global regular expression:






                const str = 'abcdefg';
                
const pattern = /(.)./g;
                
let match;
                
while (match = pattern.exec(str)) {
                
  console.log('first captured group was ' + match[1]);
                
}
                
// after the last iteration, `match` is null, so the loop stops





                If the assignment is not successful, and the cause of that non-success would throw an error, then the whole script stops due to the error. (unless there's a try / catch block around it)






                share|improve this answer















                On every iteration, it assigns the result of the foo() call to a, and if that result was truthy, it runs the loop and tries again until the result of the call is falsey.



                For example, while assigning inside a condition is generally a code smell, it's seen often enough when trying to iterate over capture groups in a global regular expression:






                const str = 'abcdefg';
                
const pattern = /(.)./g;
                
let match;
                
while (match = pattern.exec(str)) {
                
  console.log('first captured group was ' + match[1]);
                
}
                
// after the last iteration, `match` is null, so the loop stops





                If the assignment is not successful, and the cause of that non-success would throw an error, then the whole script stops due to the error. (unless there's a try / catch block around it)






                const str = 'abcdefg';
                
const pattern = /(.)./g;
                
let match;
                
while (match = pattern.exec(str)) {
                
  console.log('first captured group was ' + match[1]);
                
}
                
// after the last iteration, `match` is null, so the loop stops





                const str = 'abcdefg';
                
const pattern = /(.)./g;
                
let match;
                
while (match = pattern.exec(str)) {
                
  console.log('first captured group was ' + match[1]);
                
}
                
// after the last iteration, `match` is null, so the loop stops






                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited Jan 3 at 1:59

























                answered Jan 3 at 1:53









                CertainPerformanceCertainPerformance

                97.5k165887




                97.5k165887
































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