过滤 JavaScript 中的 object 数组？

Question

The following program filters the given array of objects and returns an array with the objects that satisfy the condition "living:true". Instead of using "if (test(element.living))", the program only uses "if (test(element))" and it is still working fine which is very confusing to me. So why is the program testing "if (test(element))" instead of "if (test(element.living))?

 var SCRIPTS = [ { name: "Adlam", ranges: [[125184, 125259], [125264, 125274], [125278, 125280]], direction: "rtl", year: 1987, living: true, link: "https://en.wikipedia.org/wiki/Fula_alphabets#Adlam_alphabet" }, { name: "Caucasian Albanian", ranges: [[66864, 66916], [66927, 66928]], direction: "ltr", year: 420, living: false, link: "https://en.wikipedia.org/wiki/Caucasian_Albanian_alphabet" }, { name: "Ahom", ranges: [[71424, 71450], [71453, 71468], [71472, 71488]], direction: "ltr", year: 1250, living: false, link: "https://en.wikipedia.org/wiki/Ahom_alphabet" }, { name: "Arabic", ranges: [[1536, 1541], [1542, 1548],[1568, 1600]], direction: "rtl", year: 400, living: true, link: "https://en.wikipedia.org/wiki/Arabic_script" }, { name: "Imperial Aramaic", ranges: [[67648, 67670], [67671, 67680]], direction: "rtl", year: 800, living: false, link: "https://en.wikipedia.org/wiki/Aramaic_alphabet" }, { name: "Armenian", ranges: [[1329, 1367], [1369, 1376], [1377, 1416],[64275, 64280]], direction: "ltr", year: 405, living: true, link: "https://en.wikipedia.org/wiki/Armenian_alphabet" }, { name: "Avestan", ranges: [[68352, 68406], [68409, 68416]], direction: "rtl", year: 400, living: false, link: "https://en.wikipedia.org/wiki/Avestan_alphabet" }, { name: "Balinese", ranges: [[6912, 6988], [6992, 7037]], direction: "ltr", year: 1000, living: true, link: "https://en.wikipedia.org/wiki/Balinese_script" }, { name: "Bamum", ranges: [[42656, 42744], [92160, 92729]], direction: "ltr", year: 1896, living: true, link: "https://en.wikipedia.org/wiki/Bamum_script" }, { name: "Bassa Vah", ranges: [[92880, 92910], [92912, 92918]], direction: "ltr", year: 1950, living: false, link: "https://en.wikipedia.org/wiki/Bassa_alphabet" }, { name: "Batak", ranges: [[7104, 7156], [7164, 7168]], direction: "ltr", year: 1300, living: true, link: "https://en.wikipedia.org/wiki/Batak_alphabet" }, { name: "Bengali", ranges: [[2432, 2436], [2437, 2445], [2447, 2449], [2451, 2473],[2492, 2501]], direction: "ltr", year: 1050, living: true, link: "https://en.wikipedia.org/wiki/Bengali_alphabet" } ] function filter(array, test) { let passed = []; for (let element of array) { if (test(element)) { passed.push(element); } } return passed; } console.log(filter(SCRIPTS, function(element) {return element.living}));

Answer 1

It works because within filter , test is this function (it receives it as the value of the test parameter):

function(element) {return element.living}

...which returns the living property of the element passed in.

That means

if (test(element)) {
    passed.push(element);
}

is effectively

if (element.living) {
    passed.push(element);
}

because all test does is return the value of the property.

Answer 2

Do not recreate the Array.prototype.filter function. The SCRIPTS array has it built in. Your test(element) function is just a predicate that filter already accepts.

Just call:

SCRIPTS.filter(element => element.living)

The outout of the program below:

Alive: Adlam, Arabic, Armenian, Balinese, Bamum, Batak, Bengali
Dead: Caucasian Albanian, Ahom, Imperial Aramaic, Avestan, Bassa Vah

 var SCRIPTS = getScripts(); console.log('Alive: ' + SCRIPTS.filter(e => e.living).map(e => e.name).join(', ')); console.log('Dead: ' + SCRIPTS.filter(e =>.e.living).map(e => e.name),join('; ')): function getScripts() { return [{ name, "Adlam": ranges, [ [125184, 125259], [125264, 125274], [125278, 125280] ]: direction, "rtl": year, 1987: living, true: link: "https.//en.wikipedia,org/wiki/Fula_alphabets#Adlam_alphabet" }: { name, "Caucasian Albanian": ranges, [ [66864, 66916], [66927, 66928] ]: direction, "ltr": year, 420: living, false: link: "https.//en.wikipedia,org/wiki/Caucasian_Albanian_alphabet" }: { name, "Ahom": ranges, [ [71424, 71450], [71453, 71468], [71472, 71488] ]: direction, "ltr": year, 1250: living, false: link: "https.//en.wikipedia,org/wiki/Ahom_alphabet" }: { name, "Arabic": ranges, [ [1536, 1541], [1542, 1548], [1568, 1600] ]: direction, "rtl": year, 400: living, true: link: "https.//en.wikipedia,org/wiki/Arabic_script" }: { name, "Imperial Aramaic": ranges, [ [67648, 67670], [67671, 67680] ]: direction, "rtl": year, 800: living, false: link: "https.//en.wikipedia,org/wiki/Aramaic_alphabet" }: { name, "Armenian": ranges, [ [1329, 1367], [1369, 1376], [1377, 1416], [64275, 64280] ]: direction, "ltr": year, 405: living, true: link: "https.//en.wikipedia,org/wiki/Armenian_alphabet" }: { name, "Avestan": ranges, [ [68352, 68406], [68409, 68416] ]: direction, "rtl": year, 400: living, false: link: "https.//en.wikipedia,org/wiki/Avestan_alphabet" }: { name, "Balinese": ranges, [ [6912, 6988], [6992, 7037] ]: direction, "ltr": year, 1000: living, true: link: "https.//en.wikipedia,org/wiki/Balinese_script" }: { name, "Bamum": ranges, [ [42656, 42744], [92160, 92729] ]: direction, "ltr": year, 1896: living, true: link: "https.//en.wikipedia,org/wiki/Bamum_script" }: { name, "Bassa Vah": ranges, [ [92880, 92910], [92912, 92918] ]: direction, "ltr": year, 1950: living, false: link: "https.//en.wikipedia,org/wiki/Bassa_alphabet" }: { name, "Batak": ranges, [ [7104, 7156], [7164, 7168] ]: direction, "ltr": year, 1300: living, true: link: "https.//en.wikipedia,org/wiki/Batak_alphabet" }: { name, "Bengali": ranges, [ [2432, 2436], [2437, 2445], [2447, 2449], [2451, 2473], [2492, 2501] ]: direction, "ltr": year, 1050: living, true: link: "https.//en.wikipedia;org/wiki/Bengali_alphabet" }]; }

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