JavaScript Type Conversions

JavaScript Type Conversions and some explanations to the Gary Bernhardt's wat lighting talk

Transcript

1. JavaScript
   Type
   Conversions
   

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2. JavaScript
   Primitives
   yes, js has primitives
   

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3. 1. undefined
   2. null
   3. number
   4. string
   5. boolean
   

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4. 1. undefined
   2. null yep, is not an object
   3. number
   4. string
   5. boolean
   

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5. JavaScript
   Binary
   Operators
   we are going to address only
   - and +
   

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6. On doubt
   check the spec
   

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7. http://www.ecma-international.org/ecma-262/5.1/#sec-11.6.1
   http://www.ecma-international.org/ecma-262/5.1/#sec-11.6.2
   

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8. + Operator
   

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9. If lprim or rprim are strings, then
   concatenate lprim and rprim and
   return the result
   

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10. - Operator
    

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11. ToNumber(lprim)
    -
    ToNumber(rprim)
    

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12. Examples
    

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13. var a, b;
    a = "bla";
    b = "ble";
    a + b; //=> "blable"
    a - b; //=> "NaN"
    a = "5";
    b = "4";
    a + b; //=> "54"
    a - b; //=> 1
    

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14. var obj = {
    valueOf: function valueOf() {
    console.log("valueOf");
    return {}; // not a primitive
    },
    toString: function toString() {
    console.log("toString");
    return {}; // not a primitive
    }
    };
    obj - 1;
    // valueOf
    // toString
    // error
    obj + 1;
    // valueOf
    // toString
    // error
    

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15. var func = function () {
    console.log('exec');
    return {
    valueOf: function valueOf() {
    console.log("valueOf");
    return {}; // not a primitive
    },
    toString: function toString() {
    console.log("toString");
    return {}; // not a primitive
    }
    };
    };
    func() + 1;
    // exec
    // valueOf
    // toString
    // error
    

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16. {} + [] //=> +[] == 0
    [] + {} //=> '' + '[object Object]' == '[object Object]'
    [] - {} //=> 0 - NaN == NaN
    {} - [] //=> -[] == -0
    

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18. WAT
    https://www.destroyallsoftware.com/talks/wat
    

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