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  1. [ References  ](/en-US/docs/Web)
  2. [ JavaScript  ](/en-US/docs/Web/JavaScript)
  3. [ Reference  ](/en-US/docs/Web/JavaScript/Reference)
  4. [ Expressions and operators  ](/en-US/docs/Web/JavaScript/Reference/Operators)
  5. [ Addition assignment (+=)  ](/en-US/docs/Web/JavaScript/Reference/Operators/Addition_assignment)

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##  In this article

  * Try it 
  * Syntax 
  * Description 
  * Examples 
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  * Browser compatibility 
  * See also 

  1. [ JavaScript ](/en-US/docs/Web/JavaScript)
  2. [ Tutorials ](/en-US/docs/Web/JavaScript/Tutorials)
  3. Complete beginners 
    1. [ JavaScript basics ](/en-US/docs/Learn/Getting_started_with_the_web/JavaScript_basics)
    2. [ JavaScript first steps ](/en-US/docs/Learn/JavaScript/First_steps)
    3. [ JavaScript building blocks ](/en-US/docs/Learn/JavaScript/Building_blocks)
    4. [ Introducing JavaScript objects ](/en-US/docs/Learn/JavaScript/Objects)
  4. JavaScript Guide 
    1. [ Introduction ](/en-US/docs/Web/JavaScript/Guide/Introduction)
    2. [ Grammar and types ](/en-US/docs/Web/JavaScript/Guide/Grammar_and_types)
    3. [ Control flow and error handling ](/en-US/docs/Web/JavaScript/Guide/Control_flow_and_error_handling)
    4. [ Loops and iteration ](/en-US/docs/Web/JavaScript/Guide/Loops_and_iteration)
    5. [ Functions ](/en-US/docs/Web/JavaScript/Guide/Functions)
    6. [ Expressions and operators ](/en-US/docs/Web/JavaScript/Guide/Expressions_and_operators)
    7. [ Numbers and dates ](/en-US/docs/Web/JavaScript/Guide/Numbers_and_dates)
    8. [ Text formatting ](/en-US/docs/Web/JavaScript/Guide/Text_formatting)
    9. [ Regular e