how does the loops blocks work

[Ahmed Alngar]

hello 

I want to know how the loops blocks work and if  I make a custom block what's the sequence of executing the code

or how it works

thanks

[Beka Westberg]

Hello,

If you want to see the code the loop blocks generate you can see that here.

If you want to see the json used to define how the loop blocks look and act you can see that here.

If you want to know about creating a custom block you can see that here.

If you want to know ways to execute generated code you can see that here.

Generally I don't like link posts because they're discouraging, but I think it was best in this case. If you have any more specific questions I'd be happy to try and help!

I hope that helps get you started,

Beka

[Ahmed Alngar]

thanks for replying Beka 

can you explain this code to me

[Beka Westberg]

Hello,

A little bit of a tricky thing about this code is that it's generating javascript for both of these blocks:

Blockly.JavaScript['controls_repeat_ext'] = function(block) {
  // This if/else statement figures out how many times the loop
  // needs to repeat.
  // If it is the top block in the picture above block.getField('TIMES')
  // will return a field, otherwise it will return null and do the else statement.
  if (block.getField('TIMES')) {
    // This figures out what the number on the top block is, and
    // converts it to a string to be used below.
    var repeats = String(Number(block.getFieldValue('TIMES')));
  } else {
    // This figures out what the number on the bottom block is, and
    // converts it to a string to be used below. For more info about
    // valueToCode see link (1)
    var repeats = Blockly.JavaScript.valueToCode(block, 'TIMES',
        Blockly.JavaScript.ORDER_ASSIGNMENT) || '0';
  }


  // This generates code for all of the blocks inside the repeat block.
  // for more info about statementToCode see link (2)
  var branch = Blockly.JavaScript.statementToCode(block, 'DO');


  // This adds a check so that the generated code doesn't loop
  // infinitely or for too long. For more info about this see link (3)
  branch = Blockly.JavaScript.addLoopTrap(branch, block.id);


  // This initialized the code variable.
  var code = '';
 
  // This grabs a name for the variable inside the for(...) statement
  // that won't collide with any user defined variables. For example
  // if the user already defined a 'count' variable, this variable would
  // be called something like 'count1'.
  var loopVar = Blockly.JavaScript.variableDB_.getDistinctName(
      'count', Blockly.Variables.NAME_TYPE);
 
  // This runs if there is a block like image (4), where the input
  // has other code inside of it. It makes sure that that code is
  // evaluated before the loop starts.
  var endVar = repeats;
  if (!repeats.match(/^\w+$/) && !Blockly.isNumber(repeats)) {
    // This grabs a name for the variable above the for(...) statement.
    var endVar = Blockly.JavaScript.variableDB_.getDistinctName(
        'repeat_end', Blockly.Variables.NAME_TYPE);
    // This adds the variable asignment before the for loop.
    code += 'var ' + endVar + ' = ' + repeats + ';\n';
  }


  // This puts all the pieces together to form the gnerated code.
  code += 'for (var ' + loopVar + ' = 0; ' +
      loopVar + ' < ' + endVar + '; ' +
      loopVar + '++) {\n' +
      branch + '}\n';


  // This returns the code so it can be added to other code strings or used.
  return code;
};

(1) : https://developers.google.com/blockly/guides/create-custom-blocks/generating-code#valuetocode

(2) : https://developers.google.com/blockly/guides/create-custom-blocks/generating-code#statementtocode

(3) : https://developers.google.com/blockly/guides/app-integration/running-javascript#infinite_loops

(4) : 

This block generates the below code:

var repeat_end = 2 + 1;
for (var count = 0; count < repeat_end; count++) {
}

For more info on generating code this page is very helpful.

I hope that helps! If you have any further questions please reply!

Beka

[Ahmed Alngar]

Thank you so much

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