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Re: [jslint] Re: option.type

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  • John Hawkinson
    Douglas Crockford wrote on Mon, 6 Jun 2011 ... This consequence appears to be undesirable: Problem at line 1 character 34: Type
    Message 1 of 9 , Jun 5, 2011
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      Douglas Crockford <douglas@...> wrote on Mon, 6 Jun 2011
      at 01:18:59 -0000 in <ish9u3+tj8c@...>:

      > Has anyone tried the new type consistency checking?
      > Has anyone found it to be useful?

      This consequence appears to be undesirable:

      Problem at line 1 character 34: Type inconsistency: string and number.

      var mixed="The value is three ("+3+")";

      An oversimplified example, but it's common to mix strings and numbers
      together knowing that the numbers will be converted to string.

      Also true for strings + booleans. It seems to fire on a lot of
      debugging statements in my code.

      --jhawk@...
      John Hawkinson
    • mathew
      ... It s a habit some programmers like to get into, because in C or Java if you forget one of the = signs by mistake you get a compile-time failure rather
      Message 2 of 9 , Jun 6, 2011
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        On Sun, Jun 5, 2011 at 21:01, Martin Cooper <mfncooper@...> wrote:

        > if (false == filePath) {
        > ...
        > var cmd = 'cd ' + filePath;
        >
        > (I don't know why the test was written like that.)
        >

        It's a habit some programmers like to get into, because in C or Java if you
        forget one of the '=' signs by mistake you get a compile-time failure rather
        than a runtime error.

        This doesn't apply in JavaScript, of course, though you're at least
        guaranteed an obvious runtime error rather than a subtle one.


        mathew
        --
        <URL:http://www.pobox.com/~meta/>


        [Non-text portions of this message have been removed]
      • spence.randall@ymail.com
        ... I gave it a try, and I was fully expecting to see a mass of errors, but was pleasantly surprised when I only had one. ... In the case of the actual error
        Message 3 of 9 , Jun 6, 2011
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          > Has anyone tried the new type consistency checking?

          I gave it a try, and I was fully expecting to see a mass of errors, but was pleasantly surprised when I only had one.

          > Has anyone found it to be useful?

          In the case of the actual error it flagged, I'm not sure. It was a "value" parameter in a setStyle function that could either be a string or a number. If the property that was being set was opacity and the browser was determined to be IE, it multiplies the value by 100 to get the proper setting for the filter. In this case wrapping the calculation in String() appears to satisfy JSLint. Would this be the proper approach?

          -Randall
        • Erik Eckhardt
          I think it s value.toString() not String(value). Correct me if I m wrong. On Mon, Jun 6, 2011 at 2:48 PM, spence.randall@ymail.com
          Message 4 of 9 , Jun 6, 2011
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            I think it's value.toString() not String(value). Correct me if I'm wrong.

            On Mon, Jun 6, 2011 at 2:48 PM, spence.randall@... <
            randall@...> wrote:

            >
            >
            >
            >
            > > Has anyone tried the new type consistency checking?
            >
            > I gave it a try, and I was fully expecting to see a mass of errors, but was
            > pleasantly surprised when I only had one.
            >
            >
            > > Has anyone found it to be useful?
            >
            > In the case of the actual error it flagged, I'm not sure. It was a "value"
            > parameter in a setStyle function that could either be a string or a number.
            > If the property that was being set was opacity and the browser was
            > determined to be IE, it multiplies the value by 100 to get the proper
            > setting for the filter. In this case wrapping the calculation in String()
            > appears to satisfy JSLint. Would this be the proper approach?
            >
            > -Randall
            >
            >
            >


            [Non-text portions of this message have been removed]
          • spence.randall@ymail.com
            Here is the code snippet in question: Original: element.style.filter = alpha(opacity= + value * 100 + ) ; Error: Type inconsistency: string and number with
            Message 5 of 9 , Jun 6, 2011
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              Here is the code snippet in question:

              Original:
              element.style.filter = 'alpha(opacity=' + value * 100 + ')';
              Error: Type inconsistency: string and number

              with String():
              element.style.filter = 'alpha(opacity=' + String(value * 100) + ')';
              No error.

              with .toString():
              element.style.filter = 'alpha(opacity=' + (value * 100).toString() + ')';
              Also no error. I think this may make the intention of the code clearer.

              Either method produces the expected result.

              -Randall








              --- In jslint_com@yahoogroups.com, Erik Eckhardt <erik@...> wrote:
              >
              > I think it's value.toString() not String(value). Correct me if I'm wrong.
              >
              > On Mon, Jun 6, 2011 at 2:48 PM, spence.randall@... <
              > randall@...> wrote:
              >
              > >
              > >
              > >
              > >
              > > > Has anyone tried the new type consistency checking?
              > >
              > > I gave it a try, and I was fully expecting to see a mass of errors, but was
              > > pleasantly surprised when I only had one.
              > >
              > >
              > > > Has anyone found it to be useful?
              > >
              > > In the case of the actual error it flagged, I'm not sure. It was a "value"
              > > parameter in a setStyle function that could either be a string or a number.
              > > If the property that was being set was opacity and the browser was
              > > determined to be IE, it multiplies the value by 100 to get the proper
              > > setting for the filter. In this case wrapping the calculation in String()
              > > appears to satisfy JSLint. Would this be the proper approach?
              > >
              > > -Randall
              > >
              > >
              > >
              >
              >
              > [Non-text portions of this message have been removed]
              >
            • Joshua Bell
              ... If value might be undefined or null you re better off using String(value). ... On the thread in general... Running some of my code through JSLint I m
              Message 6 of 9 , Jun 6, 2011
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                On Mon, Jun 6, 2011 at 3:08 PM, Erik Eckhardt <erik@...> wrote:

                > I think it's value.toString() not String(value). Correct me if I'm wrong.


                If value might be undefined or null you're better off using String(value).

                ...

                On the thread in general...

                Running some of my code through JSLint I'm (thankfully) seeing only a few
                occurrences of the "Type inconsistency" error:

                * One case where an optional argument is being tested against undefined then
                used in a string context:

                function f(a) {
                if (a !== (void 0)) {
                return "foo: " + a;
                }
                else {
                return "foo";
                }
                }

                Note that if the test is against the identifier "undefined" then the error
                goes away, it's only the "(void 0)" construction that triggers it. (I'm
                weird and don't trust the window.undefined property which is writable in
                some browsers.) This indicates that there's likely a special case for
                testing against undefined already. Arguably (pun intended) my code could
                test against arguments.length instead.

                * Construction of exception messages where a number is being concatenated
                into a string. In this case, wrapping with String() resolves the warning and
                probably improves maintainability of the code.

                * Cases where the variable is being used to hold different types, e.g. a
                string or number, and not in a type-agnostic context:

                var default_value = (var_type === 'string') ? '' : 0;

                These are infrequent enough that I can wrap them in a function and mark it
                with /*jslint type:true*/ to indicate the intent.


                [Non-text portions of this message have been removed]
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