严格模式

ES6模块自动采用严格模式(‘use strict’), 严格模式下：

  1. 变量必须声明 Object/Value
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    a = 20;  // > a=20
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'use strict';
a = 20;  // > a is not defined

  1. 不能delete 变量/Function

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    'use strict';
    var a = 20;
    delete a; // false

  2. 函数参数名不能重复

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    'use strict';
    function testParamsName(p1, p1) {
        console.log(p1); 
    }
    // 报错: Duplicate parameter name not allowed in this context

  3. 不能使用八进制字符

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"use strict";
var a = "\010";            //  报错: Octal escape sequences are not allowed in strict mode.