javascript - filter(String) also return number -



javascript - filter(String) also return number -

can explain me why filter(string) homecoming number?

class="snippet-code-js lang-js prettyprint-override">var arr = [1, "a", '7'], numarr = arr.filter(number), // homecoming 1, 7 (it's ok) strarr = arr.filter(string); // why homecoming 1, a, 7 alert("numarr = " + numarr + "\n" + "strarr = " + strarr); alert("typeof arr[0] = " + typeof arr[0]);

in illustration above, typeof arr[0] number; why it's not filtered instrarr?

thanks.

the .filter() api passes each array element value function provide. value returned function coerced boolean , tested. true results included in returned array .filter().

the number constructor interprets argument number, , returns value. when passed string "a" .filter() mechanism, returns nan, interpreted false.

the string constructor performs similar operation, key difference makes valid string. thus, number 1 in array returned "1", when converted boolean true because it's non-empty string.

to state way, not case number , string constructors perform sort of yes/no identification of numeric or string values, can't utilize them filter values in array type.

javascript

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