The function functions setting parameters in JS have a default value

I can write this in PHP

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function ABCCCC ($a =1, $b =2) { return $a + $b; }

Calls can be directly

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ABCCC () ABCCC (1) ABCCC (1,1)

But in JS this write hint hint variable undefined undefined, but I think the default value in JS should be undefined

Preset numbers in functions can be used arguments[i]

I'm the location of your argument, the first one is 0.

So to set the default value of flag, you can write this

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function func (String1,url,flag,icon) { if (!arguments[2]) flag = "123"; if (!arguments[3]) icon = "456"; }

As follows

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<script Type= "Text/javascript" Function Test (a) { var b = arguments[1]? arguments[1]:; return a + ': ' + b; } Alert (Test (5)); Alert (test 5,9); </script>