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Problem

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You want to be sure that the logic inside a function is executed only once.

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Ingredients

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Directions

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  1. \n

    Given: a function that is called twice, but should not do anything the second time it is called.

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    function printSomething() {\n  console.log('something');\n}\nprintSomething();            // (1) Ok\nprintSomething();            // (2) Should not be allowed
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    2. \n
  2. \n

    Add a variable to memorize if the function has been called.

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    function printSomething() {\n  let called = false;\n  console.log('something');\n}
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    3. \n
  3. \n

    If it is false, then return undefined.

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    function printSomething() {\n  let called = false;\n  if(called) {\n    return undefined;\n  }\n  console.log('something');\n}
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    4. \n
  4. \n

    … otherwise set the variable to true …

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    function printSomething() {\n  let called = false;\n  if(called) {\n    return undefined;\n  } else {\n    called = true;\n  }\n}
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    5. \n
  5. \n

    … execute the remaining logic of the function …

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    function printSomething() {\n  let called = false;\n  if(called) {\n    return undefined;\n  } else {\n    called = true;\n    console.log('something');\n  }\n}
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    6. \n
  6. \n

    … and overwrite the function to do nothing.

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    function printSomething() {\n  let called = false;\n  if(called) {\n    return undefined;\n  } else {\n    called = true;\n    console.log('something');\n    printSomething = function() {};\n  }\n}
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    7. \n
  7. \n

    Voilá, now if printSomething() is called a second time, it simply does nothing.

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    printSomething();        // (1) Ok\nprintSomething();        // (2) Does nothing
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    Notes

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    8. \n
  8. A function that overwrite itself is also called a self-defining function.
    9. \n
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Alternative recipes

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