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Problem

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You want to be sure that the value passed as the callback parameter is really a function.

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Ingredients

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Directions

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    \n
  1. \n

    Given: a function that accepts a callback function.

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    function someFunction(callback) {\n  callback();\n}
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    2. \n
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  1. \n

    Check that callback is of type function.

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    function someFunction(callback) {\n  if(typeof callback === 'function') {\n    callback();\n  }\n}
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    2. \n
  2. \n

    Optional: otherwise throw an error.

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    function someFunction(callback) {\n  if(typeof callback === 'function') {\n    callback();\n  } else {\n    // handle it, throw error\n    throw new TypeError('The callback parameter is no function.');\n  }\n}
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    3. \n
  3. \n

    Voilá, a delicious type check of the callback parameter.

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    someFunction(() => {console.log(4711)});  // 4711\nsomeFunction({});                         // TypeError
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    4. \n
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Variants

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Alternative recipes

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