プログラミング言語比較

出力結果

value is not defined

プログラム例

JavaScript

if (typeof value !== 'undefined') {
    console.log('value is defined');
} else {
    console.log('value is not defined');
}

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PHP

<?php
if (isset($value)) {
  print "value is defined\n";
}
else {
  print "value is not defined\n";
}

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Perl

if (defined($value)) {
  print "value is defined\n";
}
else {
  print "value is not defined\n";
}

---

Python

try:
    value
except NameError:
    print("value is not defined")
else:
    print("value is defined")

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Ruby

if defined? value
    puts "value is defined"
else
    puts "value is not defined"
end

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