JS if not a variable

2018-06-05 10:53:02

This question already has an answer here:

Is there a better way to do optional function parameters in JavaScript? [duplicate] 29 answers

如果该参数未传递给该函数，则该参数undefined 。

function foo( x, y, opt ){
    if( typeof opt === 'undefined' ){ 
        opt = 1;
    }
    ...
}

在JavaScript中，你可以添加像这样的默认值：

function foo(x,y,opt){
 if(typeof(opt)==='undefined') opt = 1;
 //your code
}

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