Contents
输出结果
value is not defined
程式码
JavaScript
if (typeof value !== 'undefined') {
console.log('value is defined');
} else {
console.log('value is not defined');
}
PHP
<?php
if (isset($value)) {
print "value is defined\n";
}
else {
print "value is not defined\n";
}
Perl
if (defined($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")
Ruby
if defined? value
puts "value is defined"
else
puts "value is not defined"
end
