是否有一个通用的JavaScript函数来检查变量是否有值,并确保它不是未定义的或空的?我有这个代码,但我不确定它是否涵盖所有情况:
function isEmpty(val){
return (val === undefined || val == null || val.length <= 0) ? true : false;
}
是否有一个通用的JavaScript函数来检查变量是否有值,并确保它不是未定义的或空的?我有这个代码,但我不确定它是否涵盖所有情况:
function isEmpty(val){
return (val === undefined || val == null || val.length <= 0) ? true : false;
}
当前回答
检查默认值
function typeOfVar (obj) {
return {}.toString.call(obj).split(' ')[1].slice(0, -1).toLowerCase();
}
function isVariableHaveDefaltVal(variable) {
if ( typeof(variable) === 'string' ) { // number, boolean, string, object
console.log(' Any data Between single/double Quotes is treated as String ');
return (variable.trim().length === 0) ? true : false;
}else if ( typeof(variable) === 'boolean' ) {
console.log('boolean value with default value \'false\'');
return (variable === false) ? true : false;
}else if ( typeof(variable) === 'undefined' ) {
console.log('EX: var a; variable is created, but has the default value of undefined.');
return true;
}else if ( typeof(variable) === 'number' ) {
console.log('number : '+variable);
return (variable === 0 ) ? true : false;
}else if ( typeof(variable) === 'object' ) {
// -----Object-----
if (typeOfVar(variable) === 'array' && variable.length === 0) {
console.log('\t Object Array with length = ' + [].length); // Object.keys(variable)
return true;
}else if (typeOfVar(variable) === 'string' && variable.length === 0 ) {
console.log('\t Object String with length = ' + variable.length);
return true;
}else if (typeOfVar(variable) === 'boolean' ) {
console.log('\t Object Boolean = ' + variable);
return (variable === false) ? true : false;
}else if (typeOfVar(variable) === 'number' ) {
console.log('\t Object Number = ' + variable);
return (variable === 0 ) ? true : false;
}else if (typeOfVar(variable) === 'regexp' && variable.source.trim().length === 0 ) {
console.log('\t Object Regular Expression : ');
return true;
}else if (variable === null) {
console.log('\t Object null value');
return true;
}
}
return false;
}
var str = "A Basket For Every Occasion";
str = str.replace(/\s/g, "-");
//The "g" flag in the regex will cause all spaces to get replaced.
检查结果:
isVariableHaveDefaltVal(' '); // string
isVariableHaveDefaltVal(false); // boolean
var a;
isVariableHaveDefaltVal(a);
isVariableHaveDefaltVal(0); // number
isVariableHaveDefaltVal(parseInt('')); // NAN isNAN(' '); - true
isVariableHaveDefaltVal(null);
isVariableHaveDefaltVal([]);
isVariableHaveDefaltVal(/ /);
isVariableHaveDefaltVal(new Object(''));
isVariableHaveDefaltVal(new Object(false));
isVariableHaveDefaltVal(new Object(0));
typeOfVar( function() {} );
我使用@Vix函数()来检查哪种类型的对象。
使用instansof«
var prototypes_or_Literals = function (obj) {
switch (typeof(obj)) {
// object prototypes
case 'object':
if (obj instanceof Array)
return '[object Array]';
else if (obj instanceof Date)
return '[object Date]';
else if (obj instanceof RegExp)
return '[object regexp]';
else if (obj instanceof String)
return '[object String]';
else if (obj instanceof Number)
return '[object Number]';
else
return 'object';
// object literals
default:
return typeof(obj);
}
};
output test «
prototypes_or_Literals( '' ) // "string"
prototypes_or_Literals( new String('') ) // "[object String]"
Object.prototype.toString.call("foo bar") //"[object String]"
其他回答
可以直接使用相等运算符
<script>
var firstName;
var lastName = null;
/* Since null == undefined is true, the following statements will catch both null and undefined */
if(firstName == null){
alert('Variable "firstName" is undefined.');
}
if(lastName == null){
alert('Variable "lastName" is null.');
}
</script>
demo@如何使用JavaScript确定变量是否未定义或为空
我想这会让你的代码看起来更简单
检查变量是否未定义或为空
var a=undefined, b=null, c='hello world', d;
if(a !== (a ?? {})) { /**/ } // true
if(b !== (b ?? {})) { /**/ } // true
if(c !== (c ?? {})) { /**/ } // false
if(d !== (d ?? {})) { /**/ } // true
检查变量是否未定义或为空
var a=undefined, b=null, c='hello world', d;
if(a === (a ?? {})) { /**/ } // false
if(b === (b ?? {})) { /**/ } // false
if(c === (c ?? {})) { /**/ } // true
if(d === (d ?? {})) { /**/ } // false
这里是我的-如果值为null、undefined等或空白(即仅包含空格),则返回true:
function stringIsEmpty(value) {
return value ? value.trim().length == 0 : true;
}
如果您喜欢纯javascript,请尝试以下操作:
/**
* Checks if `value` is empty. Arrays, strings, or `arguments` objects with a
* length of `0` and objects with no own enumerable properties are considered
* "empty".
*
* @static
* @memberOf _
* @category Objects
* @param {Array|Object|string} value The value to inspect.
* @returns {boolean} Returns `true` if the `value` is empty, else `false`.
* @example
*
* _.isEmpty([1, 2, 3]);
* // => false
*
* _.isEmpty([]);
* // => true
*
* _.isEmpty({});
* // => true
*
* _.isEmpty('');
* // => true
*/
function isEmpty(value) {
if (!value) {
return true;
}
if (isArray(value) || isString(value)) {
return !value.length;
}
for (var key in value) {
if (hasOwnProperty.call(value, key)) {
return false;
}
}
return true;
}
否则,如果您已经使用下划线或lodash,请尝试:
_.isEmpty(value)
你做得有点过头了。要检查变量是否没有给定值,只需要检查undefined和null。
function isEmpty(value){
return (typeof value === "undefined" || value === null);
}
这是假设0、“”和对象(甚至是空对象和数组)是有效的“值”。