Why doesn’t my equality comparison using = (a single equals) work correctly? [duplicate]

by

= is always assignment. Equality comparison is == (loose, coerces types to try to make a match) or === (no type coercion).

So you want

if (str === ''){
// -----^^^

not

// NOT THIS
if (str=""){
// -----^

What happens when you do if (str="") is that the assignment str="" is done, and then the resulting value ('') is tested, effectively like this (if we ignore a couple of details):

str="";
if (str) {

Since '' is a falsy value in JavaScript, that check will be false and it goes to the else if (str.length <= 9) step. Since at that point, str.length is 0, that’s the path the code takes.

More Related Contents:

  1. Which equals operator (== vs ===) should be used in JavaScript comparisons?
  2. What is the difference between the `=` and `==` operators and what is `===`? (Single, double, and triple equals)
  3. How do I check for null values in JavaScript?
  4. Why `null >= 0 && null
  5. Checking if two Dates have the same date info
  6. JavaScript Date Comparisons Don’t Equal [duplicate]
  7. How does JS type coercion work?
  8. Why does (“foo” === new String(“foo”)) evaluate to false in JavaScript?
  9. What is the difference between the = and == operators, and what is ===?
  10. Javascript – deepEqual Comparison
  11. How to check if two vars have the same reference?
  12. Determining Date Equality in Javascript
  13. Can I define custom operator overloads in Javascript? [duplicate]
  14. Reloading a single div in an html page [closed]
  15. Auto Uploading file
  16. How to initialize an array’s length in JavaScript?
  17. What is the difference between state and props in React?
  18. How can I set default homepage in FF and Chrome via javascript?
  19. Sanitizing user input before adding it to the DOM in Javascript
  20. Android WebView JavaScript from assets
  21. How to get the start and end points of selection in text area?
  22. How to take screen shot of current webpage using Javascript/JQuery?
  23. update textarea value, but keep cursor position
  24. Save canvas as jpg to desktop [duplicate]
  25. Add names of the states to a map in d3.js
  26. How can I prevent a click on a ‘#’ link from jumping to top of page?
  27. jquery/javascript: function(e){…. what is e? why is it needed? what does it actually do/accomplish?
  28. Compare two date formats in javascript/jquery
  29. Jquery delay execution of script
  30. Show values on top of bars in a barChart

Leave a Comment