The core of JSFX is custom code written in a simple language (called EEL2), which has many similarities to C. Code is written in one or more of the numerous code sections. Some basic features of this language are:

• Variables do not need to be declared, are by default global to the effect, and are all double-precision floating point.
• Variable names are NOT case sensitive, so a and A refer to the same variable.
• Variable names may begin with a _, a-z, or A-Z, and can contain numbers after one of those characters.
• The maximum variable name length is 127 characters.
• Variable names can also contain . characters, though this is used for namespaced pseudo-objects.
• There are a few predefined constant variables: $pi, $phi, and $e.
• Basic operations including addition (+), subtraction (-), multiplication (*), division (/), and exponential (^)
• Bitwise operations including OR (|), AND (&), XOR (~), shift-left (<<), and shift-right-sign-extend (>>). These all convert to integer for calculation.
• Parentheses "(" and ")" can be used to clarify precedence, contain parameters for functions, and collect multiple statements into a single statement.
• A semicolon ";" is used to separate statements from eachother (including within parentheses).
• A virtual local address space of about 8 million words, which can be accessed via brackets "[" and "]".
• A shared global address space of about 1 million words, accessed via gmem[]. These words are shared between all JSFX plug-in instances.
• Shared global named variables, accessible via the "_global." prefix. These variables are shared between all JSFX plug-in instances.
• User definable functions, which can define private variables, parameters, and also can optionally access namespaced instance variables.
• Numbers are in normal decimal, however if you prefix an '$x' to them, they will be hexadecimal (i.e. $x90, $xDEADBEEF, etc). -- (REAPER v4.25+ can also take traditional C syntax, i.e. 0x90)
• You may specify the ASCII value of a character using $'c' (where c is the character).
• If you wish to generate a mask of 1 bits in integer, you can use $~X, for example $~7 is 127, $~8 is 255, $~16 is 65535, etc.         -- REAPER 4.25+.
• Comments can be specified using:
  • // comments to end of line
  • /* comments block of code that span lines or be part of a line */

• [ ]

      z=x[y]; 
      x[y]=z;
  

  You may use brackets to index into memory that is local to your effect. Your effect has approximately 8 million (8,388,608) slots of memory and you may access them either with fixed offsets (i.e. 16811[0]) or with variables (myBuffer[5]). The sum of the value to the left of the brackets and the value within the brackets is used to index memory. If a value in the brackets is omitted then only the value to the left of the brackets is used.

      z=gmem[y]; 
      gmem[y]=z;
  

  If 'gmem' is specified as the left parameter to the brackets, then the global shared buffer is used, which is approximately 1 million (1,048,576) slots that are shared across all instances of all JSFX effects.
  
  The plug-in can also specify a line (before code sections):

  options:gmem=someUniquelyNamedSpace
  

  which will make gmem[] refer to a larger shared buffer, accessible by any plugin that uses options:gmem=<the same name>. So, if you have a single plug-in, or a few plug-ins that access the shared namespace, they can communicate without having to worry about other plug-ins. This option also increases the size of gmem[] to be 8 million entries (from the default 1 million). -- REAPER 4.6+
  
  
• !value -- returns the logical NOT of the parameter (if the parameter is 0.0, returns 1.0, otherwise returns 0.0).
• -value -- returns value with a reversed sign (-1 * value).
• +value -- returns value unmodified.
  
  
• base ^ exponent -- returns the first parameter raised to the power of the second parameter. This is also available the function pow(x,y)
  
  
• numerator % denominator -- converts the absolute values of numerator and denominator to integers (may be 32-bit or 64-bit integers depending on platform/OS/etc), returns the remainder of numerator divided by denominator.
  
  
• value << shift_amt -- converts both values to 32 bit integers, bitwise left shifts the first value by the second. Note that shifts by more than 32 or less than 0 produce undefined results. -- REAPER 4.111+
  
  
• value >> shift_amt -- converts both values to 32 bit integers, bitwise right shifts the first value by the second, with sign-extension (negative values of y produce non-positive results). Note that shifts by more than 32 or less than 0 produce undefined results. -- REAPER 4.111+
  
  
• value / divisor -- divides two values and returns the quotient.
  
  
• value * another_value -- multiplies two values and returns the product.
  
  
• value - another_value -- subtracts two values and returns the difference.
  
  
• value + another_value -- adds two values and returns the sum.
  
  
• Note: the relative precedence of |, &, and ~ are equal, meaning a mix of these operators is evaluated left-to-right (which is different from other languages and may not be as expected). Use parentheses when mixing these operators.
• a | b -- converts both values to integers (may be 32-bit or 64-bit integers depending on platform/OS/etc), and returns bitwise OR of values.
• a & b -- converts both values to integers (may be 32-bit or 64-bit integers depending on platform/OS/etc), and returns bitwise AND of values.
• a ~ b -- converts both values to integers (may be 32-bit or 64-bit integers depending on platform/OS/etc), bitwise XOR the values. -- REAPER 4.25+
  
  
• value1 == value2 -- compares two values, returns 1 if difference is less than 0.00001, 0 if not.
• value1 === value2 -- compares two values, returns 1 if exactly equal, 0 if not. -- REAPER 4.53+
• value1 != value2 -- compares two values, returns 0 if difference is less than 0.00001, 1 if not.
• value1 !== value2 -- compares two values, returns 0 if exactly equal, 1 if not. -- REAPER 4.53+
• value1 < value2 -- compares two values, returns 1 if first parameter is less than second.
• value1 > value2 -- compares two values, returns 1 if first parameter is greater than second.
• value1 <= value2 -- compares two values, returns 1 if first is less than or equal to second.
• value1 >= value2 -- compares two values, returns 1 if first is greater than or equal to second.
  
  
• Note: the relative precedence of || and && are equal, meaning a mix of these operators is evaluated left-to-right (which is different from other languages and may not be as expected). Use parentheses when mixing these operators.
• y || z -- returns logical OR of values. If 'y' is nonzero, 'z' is not evaluated.
• y && z -- returns logical AND of values. If 'y' is zero, 'z' is not evaluated.
  
  
• y ? z      -- how conditional branching is done -- similar to C's if/else
  y ? z : x
  
  If y is non-zero, executes and returns z, otherwise executes and returns x (or 0.0 if ': x' is not specified).
  
  Note that the expressions used can contain multiple statements within parentheses, such as:

   
        x % 5 ? (
          f += 1;
          x *= 1.5;
        ) : (
          f=max(3,f);
          x=0;
        );
  

• y = z -- assigns the value of 'z' to 'y'. 'z' can be a variable or an expression.
• y *= z -- multiplies two values and stores the product back into 'y'.
• y /= divisor -- divides two values and stores the quotient back into 'y'.
• y %= divisor -- converts the absolute values of y and divisor to integers (may be 32-bit or 64-bit integers depending on platform/OS/etc), returns and sets y to the remainder of y divided by divisor.
• base ^= exponent -- raises first parameter to the second parameter-th power, saves back to 'base'
• y += z -- adds two values and stores the sum back into 'y'.
• y -= z -- subtracts 'z' from 'y' and stores the difference into 'y'.
• y |= z -- converts both values to integer, and stores the bitwise OR into 'y'
• y &= z -- converts both values to integer, and stores the bitwise AND into 'y'
• y ~= z -- converts both values to integer, and stores the bitwise XOR into 'y' -- REAPER 4.25+

• ( and ) (vs { } ) -- enclose multiple statements, and the value of that expression is the last statement within the block:

       z = (
         a = 5; 
         b = 3; 
         a+b;
       ); // z will be set to 8, for example
    

• Conditional branching is done using the ? or ? : operator, rather than if()/else.

     a < 5 ? b = 6; // if a is less than 5, set b to 6
     a < 5 ? b = 6 : c = 7; // if a is less than 5, set b to 6, otherwise set c to 7
     a < 5 ? ( // if a is less than 5, set b to 6 and c to 7
       b = 6;
       c = 7;
     );
  

• The ? and ?: operators can also be used as the lvalue of expressions:

     (a < 5 ? b : c) = 8; // if a is less than 5, set b to 8, otherwise set c to 8
  

• sin(angle) -- returns the Sine of the angle specified (specified in radians -- to convert from degrees to radians, multiply by $pi/180, or 0.017453)
• cos(angle) -- returns the Cosine of the angle specified (specified in radians).
• tan(angle) -- returns the Tangent of the angle specified (specified in radians).
• asin(x) -- returns the Arc Sine of the value specified (return value is in radians).
• acos(x) -- returns the Arc Cosine of the value specified (return value is in radians).
• atan(x) -- returns the Arc Tangent of the value specified (return value is in radians).
• atan2(x,y) -- returns the Arc Tangent of x divided by y (return value is in radians).
• sqr(x) -- returns the square of the parameter (similar to x*x, though only evaluating x once).
• sqrt(x) -- returns the square root of the parameter.
• pow(x,y) -- returns the first parameter raised to the second parameter-th power. Identical in behavior and performance to the ^ operator.
• exp(x) -- returns the number e (approx 2.718) raised to the parameter-th power. This function is significantly faster than pow() or the ^ operator
• log(x) -- returns the natural logarithm (base e) of the parameter.
• log10(x) -- returns the logarithm (base 10) of the parameter.
• abs(x) -- returns the absolute value of the parameter.
• min(x,y) -- returns the minimum value of the two parameters.
• max(x,y) -- returns the maximum value of the two parameters.
• sign(x) -- returns the sign of the parameter (-1, 0, or 1).
• rand(x) -- returns a psuedorandom number between 0 and the parameter.
• floor(x) -- rounds the value to the lowest integer possible (floor(3.9)==3, floor(-3.1)==-4).
• ceil(x) -- rounds the value to the highest integer possible (ceil(3.1)==4, ceil(-3.9)==-3).
• invsqrt(x) -- returns a fast inverse square root (1/sqrt(x)) approximation of the parameter.

• loop(count,code)

        loop(32, 
           r += b;
           b = var * 1.5;
        );
      

  Evaluates the first parameter once in order to determine a loop count. If the loop count is less than 1, the second parameter is not evaluated.
  Be careful with specifying large values for the first parameter -- it is possible to hang your effect for long periods of time. In the interest of avoiding common runtime hangs, the loop count will be limited to approximately 1,000,000: if you need a loop with more iterations, you may wish to reconsider your design (or as a last resort, nest loops).
  
  The first parameter is only evaluated once (so modifying it within the code will have no effect on the number of loops). For a loop of indeterminate length, see while() below.
  
  
• while(code)

         while(
           a += b;
           b *= 1.5;
           a < 1000; // as long as a is below 1000, we go again.
         );
      

  Evaluates the first parameter until the last statement in the code block evaluates to zero.
  
  In the interest of avoiding common runtime hangs, the loop count will be limited to approximately 1,000,000: if you need a loop with more iterations, you may wish to reconsider your design (or as a last resort, nest loops).
  
  
• while(condition) ( code ) -- REAPER 4.59+

         while ( a < 1000 ) (
           a += b;
           b *= 1.5;
         );
      

  Evaluates the parameter, and if nonzero, evaluates the following code block, and repeats. This is similar to a C style while() construct.
  
  In the interest of avoiding common runtime hangs, the repeat count will be limited to approximately 1,000,000: if you need a loop with more iterations, you may wish to reconsider your design (or as a last resort, nest loops).
  
  
  
  

• time([v]) -- REAPER 4.60+
  Returns the current time as seconds since January 1, 1970. 1 second granularity. If a parameter is specified, it will be set to the timestamp.
  
  
• time_precise([v]) -- REAPER 4.60+
  Returns a system-specific timestamp in seconds. Granularity is system-defined, but generally much less than 1 millisecond. Useful for benchmarking. If a parameter is specified, it will be set to the timestamp.