How does plus equal work

Question

I m a bit confused with the    sign  How does it work    1    2    equals   and this  var data    1 2 3 4 5   var sum   0  data forEach function value        sum    value       sum

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operator is used to concatenate strings or add numbers   It will increment your sum variable with the amount next to it   var sum   0  var valueAdded   5    sum    valueAdded       sum   5

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a    b is shorthand for a   a  b which means   1  1    2    won t compile  2  15

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x    1 is just shorthand for x   x   1 It can also be used for strings  var string    quot foo quot  string     quot bar quot

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NO  1  2  2 it means  you are going to add 1 2  But this will give you a syntax error  Assume if a variable is int type int a 1  then a  2  means a 1 2  and increase the value of a from 1 to 3

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in JavaScript  as well as in many other languages  adds the right hand side to the variable on the left hand side  storing the result in that variable   Your example of 1   2 therefore does not make sense   Here is an example   var x   5  x    4     x now equals 9  same as writing x   x   4  x -  3     x now equals 6  same as writing x   x - 3  x    2     x now equals 12  same as writing x   x   2  x    3     x now equals 4  same as writing x   x   3    In your specific example the loop is summing the numbers in the array data

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To be precise a  b not actually equals to a   a   b  It actually is a   a    b   How so  Let me show you a demo   x000D   x000D  a   1  console log  a    1 lt  lt 2     a    1 lt  lt 2      results in 5  a   1     If a    b is equal to a   a   b then this would be 5  But as you see this is not  The result is 8  console log  a   1  lt  lt  2     a   1  lt  lt  2      results in 8   a   1     As you can see this results in 5  console log  a    1 lt  lt 2      a    1 lt  lt 2       results in 5 x000D   x000D   x000D   Because this     or    or -  or    etc operators implicitly groups the right hand side

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That is just a short form for   sum   sum   value

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x  y is shorthand in many languages for set x to x   y   The sum will be  as hinted by its name  the sum of the numbers in data

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1    2 won t throw an error but you still shouldn t do it  In this statement you are basically saying  quot set 1 equal to 1   2 quot  but 1 is a constant number and not a variable of type  number or  string so it probably wouldn t do anything   Saying var myVariable   1 myVariable    2 console log myVariable   would log 3 to the console  as x    y is just short for x   x   y  var data    1 2 3 4 5  var sum data forEach function value     sum    value     would make sum   15 because  sum    1   sum   1 sum    2   sum   3 sum    3   sum   6 sum    4   sum   10 sum    5   sum   15

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that s just a shorthand notation in most languages which means that      x x 1    we can do the same operation for x- 1 x  1 x  1  which means    x x-1  x x 1  x x 1

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As everyone said above  x000D   x000D  var str    foo  str      bar  console log str    will now give you  foo bar  x000D   x000D   x000D   Check this out as well https   www sitepoint com shorthand-javascript-techniques

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1    2 is a syntax error  left-side must be a variable    x    y is shorthand for x   x   y

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1  1    2    equals     That is syntactically invalid  The left side must be a variable  For example   var mynum   1  mynum    2     now mynum is 3    mynum    2  is just a short form for mynum   mynum   2   2   var data    1 2 3 4 5   var sum   0  data forEach function value        sum    value         Sum is now 15  Unrolling the forEach we have   var sum   0  sum    1     sum is 1 sum    2     sum is 3 sum    3     sum is 6 sum    4     sum is 10 sum    5     sum is 15

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and don t forget what happens when you mix types   x   127  x      hours      x is now a string   127 hours   x    1     0     x is still a string   127 hours false

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You have to know that    Assignment operators syntax is  variable   expression   For this reason 1    2 -  1   1   2 is not a valid syntax as the left operand isn t a variable  The error in this case is ReferenceError  invalid assignment left-hand side  x    y is the short form for x   x   y  where x is the variable and x   y the expression    The result of the sum is 15           sum   0        sum   sum   1     1       sum   sum   2     3       sum   sum   3     6       sum   sum   4     10       sum   sum   5     15   Other assignment operator shortcuts works the same way  relatively to the standard operations they refer to

[javascript] How does += (plus equal) work?

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